I own 5 VsTanks and must say they are of the highest quality. Any of them can fight the others, so feel free to buy 4 of the same model if that's what you want. The crystals are proprietary as far as I know, but they have around 15 available. The only word of caution is that these are highly detailed models with lots of bits that will break off. I have come to expect the tiny detail parts to be lost when I let the neighborhood kids join the battle. If you plan on use oj carpet, do not get the T-72. It's one of their best, but the rubber tracks grip too well and come right off the wheels. I also suggest buying 8 AA nimh batteries for each tank for longer runs and huge savings. Alkalines last about 2hrs.