Hey C No 7 Mk 1, I'm new to the forum but have been soaking up it's knowledge for a long time, so I'm glad to be able to give back!
I'm so amazed with the capability of 3d printed items. The BR is sturdy, he chose to use bolts and nuts to secure items into the 3d printed frame so that it's metal to metal, making it capable of handling some torque when you assemble without worrying about snapping anything. I'm normally guilty of over-torquing but didn't worry with this style of nut and bolt set up to secure the "buffer tube" to the frame for BR. As far as loading the bipod, I'd say you probably would be issue-free. There is going to already be less flex than the OEM plastic stock as thats kinda flimsy. With the tri rail, you'd have a decent length that's attaching all the tubes (2 air, 1 barrel shroud for 10 inches) together. Plus, I think it said on BR site that there's a % discount if you order the whole kit. As you saw, I did not order the tri rail as I'm doing a bottle set up. However, from the photo and more so the YouTube install, it seems very solid being that long and I like how it has those few screws to clamp it down. I don't think it'd need reinforcement, but I suppose you could get those metal picatinny height risers on Amazon, the ones that are a 1 piece that clamp onto a section of picatinny rail for a few inches. Then you'd be clamping to metal. But it's probably not necessary.
If you don't go for the tri rail due to weight, you definitely want a triple tube barrel band to keep everything secure. I'd stick it furthest out towards the muzzle as possible. There's a few available on eBay that are 3d printed. I think I'd go for this one from dadr-232
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But it's $9 more than the BR and you get a lot less rail slots as well as the BR protects your air tubes more. Plus if you're doing all BR there's that 10% off the whole kit deal. FYI Just checked and BR is sold out til tomorrow.
If you're punching paper on a bench, you might even consider doing a double tube barrel band just before the fill cap by the muzzle to keep it all secure way out there, too.
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(Look at photo #6, this is how you should set up the bands if not doing the tri rail) others are also available on ebay or people here recommend Black Arts brand band.
As far as the AE Swede version, I guess you have 2 options. You can either unscrew the whole frame (like 2 screws) and take that off to get access to the hammer spring adjustment, or you could leave the frame on (recommended so grip is still on and less risk of POI shifts taking the whole frame off) and unthread the buffer tube to gain access. There's holes in the frame for access through to the HS directly behind the buffer tube threads. I did not like the idea of unthreading it a lot since it screws into the 3d printed frame even though the Swede frame is thick, very solid, and reinforced, and also a dude on YouTube recommended the AR folding adapter.
And so I found that adapter. Definitely a chinese version, but it's not an AR with recoil so I wasn't worried.
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I had to add a tiny spacer in the hinge to get it to the tension I wanted when folded but that was just me being picky and it didn't matter. Lock up was decently solid, couldn't tell the flex of the folding adapter over the flex of my super generic AR stock on the buffer tube. You can find that folder on places like Wish or AliExpress too just know how to look. One I bought already has listing down so I couldn't send that exact one. Same thing though.
Basically though, no technically not required. Just nicer to have so you fold, adjust HS, unfold, go. But it's not every time you shoot that you'll adjust HS. So really up to you. It was also a "Cool Factor" by having a folding stock.
You could also get a buffer tube with the hole in the back and enlarge that slightly and get a really long Allen key and put it through there to the adjustments without removing or folding anything. Idk how long that would have to be, maybe a foot long to reach all the way lol
All this is why I said it really is a wash for price because once you decide to go tactical stock, it gets to personal preference and you need certain things for one brand over the other. Again, lots of pros/cons with both of these 2 offerings for Avenger tactical stock. But you're still cheaper than Terminador Tac Stock at $150 or whatever for just the frame.
Any more questions?