The R2's are still available from the US distributer and dealer, EliteLED.COM. When their current supply of R2s are gone, they will be getting any more. I have purchased a few lights from them. They are quite reliable and ship lights out very quickly.
The R2s are probably going to be more desirable than the Q5's which tend to be slightly less bright and a bit more cold than the R2s, although there are variations in tint with all LED's. LiteFlux has just begun to substitute the Q5's in the LF5xt, because they are unable to get sufficient quantities of the R2 as they had been able to do in the past. The Q5's to my knowledge, while being made, have not been received and reviewed. So any difference is just conjecture on my part. What isn't conjecture is the list price on the Q5 version has been lowered to $62 list (see LiteFlux.com). The R2's are currently going for $69.95.