Update: I used the wrong size torx bit when installing a rail. One size too small. Twisted the bit, not beyond use, but lesson learned to be more careful, it felt like a fit. Used a T9 when I should have used a T10. I was worried that these might have bits that are too hard and will end up stripping screws, unlike what the Magna-Tips from Brownells are supposed to do (break the bits to preserver the screws), but it may be the bits will give out before a screw head will end up being stripped.
While not stated in the linked pages, the 72 piece set has the following for the bits: made from durable S2 tool steel with a 56-58 Rockwell "C" hardness rating.
Presumably all their bits are the same across all kits, except for specialty kits like the Precision Micro kit which has chrom plated steel bits.