There are a couple of designs for M14 mags.
G&G and Classic army have a cut-out at one end and won't take TM style mags.
Gas guns use a lipped variant and are model specific.
All of the other companies use the standard full top mag like the one you linked.
The ones you have picked should be fine.
Patrol base have high caps at a decent price as well.
http://www.patrolbase.co.uk/airsoft/asg-400-round-m14-slv-aeg-hi-cap-magazine-black.htm#.WsSdPn_TVes
Mid caps need to be sprayed with silicone oil internally, then filled and emptied.
You fill them bit at a time, so 10bb's in, empty it, 20 bb's in empty it, 30 bb's in, empty it. More spray, 40 in, empty, 50 in, empty, oil, 60 in empty. You do this so the spring compresses correctly and you get an even oil coverage on the plastic walls where the plate on the top of the spring slides.
It helps if when you spray you use a small screwdriver to push the plate in a little So the oil goes past the plate.
The BB's you use need to be separated from your normal stock, and thrown away after or kept separate for if you do another mag. If you try to shoot them it'll put loads of oil onto the bucking. If you don't oil the mag it might stick when it feeds so it's worth doing. Once done you can pretty much ignore any special requirements until you encounter problems, then it's a strip clean and re-oil.
Always store mid caps empty as it stops the spring getting weaker in storage.
