I have an older iteration of the REI Panniers and had another set before these. (REI replaced the first set after about 6 years when a seam opened up.) Both sets were very good, basic panniers. I switched from a backpack to these perhaps 15 years ago, and I would never go back. I use them pretty much the way the OP wants to use panniers, though my commute is a bit longer and I carry loads of books, too. (I am amazed at how many groceries I can get in them.)
The bags are pretty water resistant, but you'll need to put dry stuff in plastic bags (I use a trash compacter bag as a liner for the whole pannier) when the weather is wet or slushy. Easy on and off. Mine have a front pocket that was just big enough to hold a u-lock and cable - that is convenient. I don't see that pocket in the picture - is it now on top? If you intend to carry a computer, make sure it will fit. My computer cannot fit inside the pannier when in the manufacturer's carrying case and some laptops wouldn't fit in the panniers at all. The REI guarantee is great.
Here's a few other things to know: 1) The ends of the compression straps can flap around and end up in the spokes if one does not tuck them someplace. This is noisy and annoying but nothing more. That little plastic hook that looks like it should secure the ends is not a solution. On the contrary, it seems to always be in the wrong place, either impeding the expansion of the bags or making compression difficult. You will probably end up not using the hook. If I have the bag compressed, I just tuck the end of the strap between strap and bag; 2) The little screw that one uses to adjust tension on the horizontal hook - you can see it in the picture - has disappeared two times - but that's over many years; 3) the backplate can bend inwards when you are carrying a small heavy load unless you use care to pack the load carefully and tighten the compression straps just right. Twice I have had the backplate bend enough so that when I was out of the saddle rocking the bike, the edge of the backplate ended up in the spokes. Each time the pannier came flying off in the middle of an intersection. Once the spokes were damaged. (That incident is the main reason I decided to try the Arkel Commuter. The Arkel backplate is not significantly stiffer but the Arkel is shaped and packs differently. My comments on that bag are
here.); 4) These panniers are somewhat awkward to carry when off the bike but no more than any other standard pannier. The carrying strap is big enough for my whole hand but is just a flat piece of webbing - not painful but not comfortable. Since the handle is on the back edge of the bag, the bottom of the bag will hit your leg if you have a significant load.
I've been very happy with mine.
If I were buying another pannier, and still had the money I spent on my Arkel Commuter, I'd really like to take a look at the Carradice Bureau or A4 before I decided. There's a review of the Bureau here:
http://www.etherfarm.com/synapse/arc...e_bike_bureau/
I'd like to see those hooks on the back, see how heavy those bags are, and figure out what one must do to keep them waterproof.