Can I use this in a regular D8? If so, will it be super bright as it is with the rechargeable kit?
That is how I used it, and yes it is super bright. Does burn up the ole batteries pretty fast though. I'd get about 2 hours of super bright, followed by maybe 4 hours of pretty bright (about like the regular bulb) and then I'd replace the batteries (or recharge the rechargeable D's I put in there sometimes. The only problem with those is that they are pretty light making the light positively buoyant which drives me crazy).
Yes it will be as bright, bring extra batteries... you will need them.