I have a TRR8, which is the detachable bottom rail version of the R8. Also had a loose barrel nut, but i made a spanner wrench and it's been fine ever since retightening.
I like the concept of having a weapon light, but the positioning of the light is much further forward than on my auto pistols. Makes activating the light in short bursts much more awkward.
The top rail does allow the use of quick detach optics whilst retaining the iron sights. And somewhat more flexiblity in optics choices than having the rail machined integral to the barrel shroud.
But I think I'd be more comfortable with a stainless or blued steel frame. Can't give you a good reason why, though!