The R2 is probably not really 290 lumens.
I don't see why the Eagletac would not be suited to use on a shotgun, since one of its intended uses is on firearms. It may be a new product, but that does not mean that it is worse than a surefire. Just because you have never heard of anyone using one on a shotgun does not mean that it won't perform well on one. In all honesty, LEDs are very shock resistant, and The T100C2 seems like a very durable light, so I don't see why it wouldn't work fine.
My problem with surefires is this: In stock form, most are outdated and overpriced. In order to bring them up to date, you have to spend additional money to get a good dropin (like $55 for a malkoff), and you can't fit an 18650. There are other P60 hosts out there for less than a surefire that would work fine, and fit 18650s. If you are going to get a Z49 anyway and replace the stock surefire dropin, then you might as well get something like a Solarforce L2 host without a dropin, and put a surefire tailcap on it, along with a Malkoff. Buying a surefire light and swapping out everything that makes it a surefire is a complete waste of money in my opinion, unless you get a used one. However, it will be used, so it might not be as reliable, and it still won't be able to fit 18650s.
Also, I see no reason why Lithium Ion cells would be any less reliable than CR123's in a combat situation. They have virtually no self discharge, more capacity than CR123s, and can be topped off to ensure that they are always fully charged, which can't be done with primaries.