Since the SPD cleats are most of the time in the shoes' sole, they will basically last forever (or at least, a lot more than SLs). On their side, SPD-SL cleats are a little more capricious. You need to change them whenever they're worn out. You'll know.

Regardless, I think you're overthinking this whole cleat thing. Just use SPD-SL if you are into road cycling, long rides & climbs, and use SPD if you're an all-arounder who prefers something a little more versatile. Also try both and see what you prefer most.

Unless you're close to being a professionnal cyclist, the weight argument is pointless in my opinion. You'll most likely not notice any difference at all...

Yes. And no. It depends.

The "right" amount of float is good, more than that amount is bad and can cause injury.

Float needs are specific to each person. If you have stable feet that don't pronate or supinate, float won't matter much.

"Knee pain is caused by too much float as often as it is caused by a lack of float."

Another thing about float: the bigger the float, the more you have to rotate your foot to unclip from the pedal. I tested some 9º float Look Keo cleats, but they required a massive effort to unclip. Now I use 6º float cleats, which I find much easier to clip out.

I was in your shoes 2 months ago. I had been riding flats for 6 months and had been hesitant to make the switch to cleats. It has already been sussed out in this thread, if you want to walk more comfortably when not clipped, go SPD. They are dual sided and easier to get into. I have found really no advantage to SPD SL over SPD in leisure riding applications. As previously noted, if you plan to get dirty/muddy, SPD will work more reliably IMO.

That being said, I road bike the most and I wear SPD SL. I like the feel, the look, and the shoes. It's just what I feel good in and when I feel good, I will ride. I fell over twice and suffered a blow to my ego, but now I'm a bit of a natural (which is fortunate). I wish I had made the switch earlier but I don't think using cleats is like revolutionary to your cycling experience. But YMMV! Good luck.

It happens to me at least 1x per season. Doesn't get any better with the years. This year, I was a traffic light after a good climb (exhausted and out of breath) and missed the light post while trying to grab it to lean against it - I fell on the side slowly. You just gotta keep your sunglasses on when you get back up & people are starring at you. That's why I won't go with SPD-SL when I'll buy a commuter bike. Dual sided SPDs for the win!

Ease of entry is a bit of a BS argument for road. On road, you're stopped. When stopped, an SPD-SL pedal will naturally rotate with gravity to the same exact spot every time for an easy entry.

An SPD does not. An SPD shines in terms of shedding muck AND being able to clip in and out in dynamic (in motion) situations.

Even if you could run in a hypothetical SL cleat, and hypothetically it didn't take on muck......in a cross race on a dismount/remount you can't depend on gravity to return the pedal to a good entry point. Here, the SPD being dual sided wins out. Or 4-sided if you're an egg beaters rider.

Or in MTB if you're unclipping an inside leg during a slide in a corner or something.

I argue for a fitness oriented road rider to go with SL's simply for the ability to use the same shoe and same pedal on multiple type bikes and be able to comfortably walk anywhere you want to. And durability of a hidden metal cleat.

If I had to pick a commuter pedal/shoe, it would be a really comfy lace up and a combo flat/SPD setup where it's got the little cage around an SPD pedal.

Why SL's for road then? They're quite a bit lighter. Combined with a dedicated carbon road shoe I'd bet an SL setup could be a full pound lighter than an SPD shoe with sole and SPD metal pedals. Maybe not a pound, but it's a LOT.

That's my $0.02.

These Sidi adapter plates are a much better product than the shimano and wellgo adapters (tried them both). It fits Shimano, Cronos and Specialized.

I just went through this for my first set of clipless. The summary I have is that -SL is more efficient and potentially more comfortable on longer rides. However, both of those advantages are reduced with stiff shoes. An advantage still exists, but unless you are pushing for that last bit of power and efficiency, you are unlikely to notice it.

For me, I ended up with SPD. I only ride on the road (although it is current a Hybrid) with no real desire to offroad. When I commute, I have to stop at one light and walk maybe 30 steps in total. -SL would have been a fine choice, but my LBS had a pair of old model XC7 on sale for almost the same price as the cheapest road shoes (and they are stiffer), so I went with it. If my engine is ever upgraded so much that I need that last bit of power and efficiency, I'll look into road shoes and 3 bolt pedals, but until then I suspect my solution is more than adequate.

Plus, if I start doing those spin classes in the winter I have shoes that work!

Okay, I've decided to stick to SPD, reason being is cause I do have some steep paved farm roads which are used by MTBs, but it's possible to ride a road bike on it, but you'll need to be trained to ride up it. With the popularity of gravel, I expect more stylish SPD shoes on the horizon, or I'll just get a Bont Vaypor G which is essentially the same as their road shoes except with SPD cleats

Those look great! I am using metal SPDs on my winter boots because the 3-hole drilling is way too far forward for me, but the 2-bolt slots are in the right place. I'll have to see whether those will line up without too much alteration.

Interesting, they’re dual sided SPD pedals that are lighter than even road pedals for those weight weenies out there.

https://xpedo.com/product/pedals/mtb/m-force-8/

lighter than even Shimano Dura Ace road pedals which is really impressive considering one is mainly made out of composite plastic and another is mainly metal.

And I've read the reviews and it seems to perform well.