I took 30 USGI 30 round magazines which I bought during the band and rebuilt them. I selected the magazines which were in the best shape and all 30 were practically in brand new condition, but technically used. Some needed to be rebuilt, but most didn't so I did them all to be safe. I purchased 3 or Tapco's 30 round magazine revitilizing kits which included 10 springs, 10 followers and 10 dust covers per kit. The springs/followers are identical to USGI componets and function is the same. I was able to rebuild 30 magazines and return them to brand new condition for less than 60.00 which is much cheaper than I could buy 30 USGI magazines. While Tapco makes some real junk, these kits don't fall into this category. These magazines function everybit as well as my D&H, Okay or Center Industries LEO and are everybit as reliable. While I have 20 or so seperate defensive magazines which consist of brand new D&H/Cproducts/Okay/Center I would have no problem using these as defensive magazines. These are my practice magazines and I have fired thousands of rounds through them without any problems. The only thing I have noted is the Tapco green follower isn't as "soft" as USGI green followers. The Tapco follower is a green, anti-tilt design but it appears to be made of the same material as the older "black" follower which could make it more brittle. I have dropped several loaded/unloaded magazines and have yet to have one breakage while I have broken the followers of 3 SA80 steel magazines after dropping them on the pavement while fully loaded.
To increase my supply of "defensive" magazines, I was going rebuild 10 of mint condition Labelle/General Stamping magazines with IMSI or Wolff Springs and Magpul followers. I figured I could do this for 7.00 per magazine. Brand new Cproducts magazines with CS springs and Magpul Gen 2 followers are 10.50. With magazines so, cheap it doesn't make sense to rebuild magazines, unless they are rare/desierable like USGI 20's or FNC magazines. Magazines won't be this cheap forever, so stock up now while you can or you will regret it. Personally, brand new magazines are preferable to rebuilt/used magazines. I ordered 8 Cproducts magazines with orange magpul followers today to increase my supply of defensive magazines. I intend to order at least 3 more lots of 8 magazines, configured the same way. Magpul followers are an improvement over USGI green followers, and they can increase reliability of the magazine. I have never had a problem with "black" followers, let alone "green" followers. Personally, I think a stock grey/black D&H magazine is as good, if not better than any other magazine. I haven't had problems with my D&H magazines or thier followers, so I don't consider Magpul followers to be a "mandatory" upgrade.
I think you should consider the Tapco revitilizing kit for your magazines. Its very cost effective and provided you start with good magazines, they will be as functional and reliable as a stock D&H or NHTMG magazine even if the kit did come from Tapco. For 20.00 you get 10 springs/10 followers/10 dust covers in a paratrooper pouch, wich holds like 18 magazines and can attach to your belt. Some might say that USGI 30 round magazines with IMSI/Wolff springs and Magpul followers are better/more reliable than standard D&H/Okay/Brownells/Larsen etc magazines. I don't necessarily agree, but I give credit where credit is due. The improved springs/followers can make for a more reliable magazine, but I have found brand new USGI contract magazines to be 100% reliable and while the modifications are nice and could potentially help, I don't consider them mandatory. While I will have 24 Cproducts magazines with orange Magpul followers, I am not about to tear into 70+ magazines which have never given me any problems just to instal Magpul followers. While they can improve function/reliability, USGI 30's have been working well for years all over the world, even with "black" followers. The 12 magazines my friend carried into battle in Iraq looked abhorent, some of which had "black" followers. He reported they all workd 100% and he experienced no problems. Only you can decide whether its worth it or not....they are nice, but not mandatory for me.