I don't know how much it costs but Tectonic Quake 8/Oshiboom BFG has better value simply because it holds more primers. I've got an oshiboom and it's amazing at least for indoor purposes.
If I'm restricted to one shot I'd invest into Dynatec/SWAT VTG. At least those ones are always go off regardless the surface. Impact grenades have a tendency not going off even on hard surface let alone outdoor.
Krytac P90 is awesome (I have one) but it's way too expensive for a first gat. P90 isn't gonna be ergonomic for everyone just keep it in mind.
As above mentioned either Novri or Marui P90+ if you really keen on that platform.
I wanted to say focusing mainly on Maruis might be not the best business decision when people are more skint than ever but then I remembered that Eagle6 is doing just fine.
I don't think that any of the skinny handguards support batteries there is literally no space between them and the outer barrel. It's not a show piece though because you can sell it with some loss obviously. Lots of people are into RS stuff here and it's a drop-in in most cases regarding gbb mp5's.
I bought a cheap clone of that particular handguard and had the same issues. Your best bet is the genuine magpul handguard or if you feel adventurous you could try something like this:
https://www.sixmm.com/en-gb/products/army-force-mp-style-mp5-m-lok-handguard-for-tokyo-marui-mp5-ngrs-gbb-seriesblk.
LCT is extremely overpriced crap without mosfet and decent internals. Yes, externally might be superior to others but in 2025 that's simply not enough when a sub 200 pound specna knows pre-cocking and programmable by few trigger pulls.
I use GBBR on HPA. Best of both worlds for me coz it's cost efficient and temperature doesn't matter. It's not as fun as a vanilla gas gun because it donesn't lock back on empty and reloading is less tacticool but I don't care personally.
The other thing with gas guns that I'm not gonna spend another 500 pounds on 8 gas magazines each time I buy something it's ridiculous...
I had a Gen.5 for a few months or so and I sold it because it's just another glock at the end of day. I understand that when you crave it it seems way better then what it is but I think it's extremely overhyped/overrated. ?♂️
I think it's more about the paper work from the seller's side than anything else. I bought at least a few guns from HK and never had an issue like this.