The small bike light I used before I bought flashlight has two small lenses on the side, so the visibility from the side is very good. My new flashlight, I believe like all or most others mentioned here, doesn't have this feature, which I noticed on first use. That's because they were not designed for bike use. So they are not perfect. Room for improvement and opportunity for innovations

I use a white flashing blinky bike light or two (like a bike tail light only white instead of red light) on the front in addition to the flashlight headlights. This provides "to be seen" visibility from the side and also gives me some side illumination "to see" as well within a 10-foot radius or so although there is a "step-jerk motion" strobe effect when observing things to the side if there isn't any other light sources

Only speaking for myself, but the flashlights I use, can be seen from all angles, even the rear!! How does it do this? Again, only speaking for myself again, the flashlights I use put out such a large footprint, it can be seen at all angles. I have had cars come up from behind, and want to know what this was..

See for yourself..

What I call the "footprint" is the light shining on the ground. On my lights, they can see that big time from the rear and from the side. From the front, coming toward me, it is like a trip to the sun!!

Nice. How many lumens?

side visibility (or lack thereof) is one of the things that tends to separate "see lights" from "be seen lights". most high-output "see lights", even bicycle specific ones, do little or nothing to increase conspicuity from the sides. all decent "be seen lights" throw some light to the sides.

if you're on the road, you should always have a "be seen light" up front. add a "see light" as needed.

my biggest problem with using a high-output flashlight as a "see light" is that it doesn't have a battery indicator... but i can solve that problem by carrying a spare 18650.

My Viz 360 has the side lights, but I don't think people would see them until ti's too late. My Magicshine puts out enough light for others to see me coming in the dark anyway.

I am pushing the Chinese clones flashlilghts, they really overstate the lums. .. With that said, the one above might be rated at 1300 lums. I think it is an honest 900 to 1000 lums, and plenty bright. In addition, that photo I was just testing it, I always run in pairs, and since it is getting dark early, one on my helmet too. Also, I am running cheap blinking light strips on my legs..

Back to this thread... I was thinking, if you make sure the taillight(s) have good side visibility, it's fine without side light in the front? (of course, agreed the more the better)

Australians come up with some pretty good ideas and AyUp lighting is a great example. Their solution to rear light visibility is to 'cap' their lights with colored extensions that give excellent 180 degree visibility. The red Saxon Caps are here https://www.ayup-lights.com/products/134/

No guarantee they'll fit all flashlights, but they'll likely fit some and give more light than most tail lights. No dimensions are given onsite.

The red caps on the AYUPs make them quite dull in comparison to say a "normal" 1/2W or 1W blinky like PBSF of Cygolite Hotshot. Considering the AYUPs are ~$250 for the most basic kit it makes them poor value for a rear light. For a front light they are great, just not that good for rear.