Im old school, I wait for the bolt to lock back LOLI use all windowless mags. The last two rounds in my mags are tracers. I'll know when I have an empty mag with one in the chamber. I bought a huge pile of tracers right before Sandy Hook at $8 a box. Got my friends and my sister to buy around a thousand each too.
LOL had me going with the whole weight different thing, from just one bullet lol.I go windowless for opsec. The spotter for an enemy sniper can view your round count from a distance and relay the information. To keep track of my round count, I've trained myself to detect the difference in weight each round makes. So I can just hold my rifle and know. For the sake of fair disclosure, I just made all that up. I buy windowless and just practice fast reloads. I guess I'd keep track of rounds in my head if I got down to my last mag in a fight. Probably not though. Adrenaline typically destroys most minor details in a plan. To be honest, I mostly buy windowless because I'm mildly OCD about my gear and want it to match.
I do the same for the most part. I feed my rifle from the left pouches (right handed) when the shooting stops I basically shift full mags to the left. Time permitting top off mags from mags that were partially used U should ALWAYS have a full magazine in ur gunI buy what ever is available and is cheapest. Most of the time that is the windowless pmag, sometime it isn't though. So for every 10 mags I have 2 of them with windows.
As far as knowing how many rounds are in the mag? It's not really reliable I have found trying to count rounds. There are so many things going on that you will be hard pressed to count. I'm talking real world shooting. Not range time. However, I try, try being the key word, to keep up with how many rounds I have discharged. With that being said, I train to change the mag when I stop shooting and I'm under cover. No matter if I have only sent 5 rounds down range. When in doubt change the mag out. I put the not empty mags in my dump pouch and if for some reason run out of full mags then I go to them.
Just how I do things.