I use them for cleaning my ARs mostly. The bolts especially. 1911 barrels too are quickly cleaned in them. They are also great for brass. I've not done as you are suggesting but I dont see why not. Have to rinse everything with water afterwards.
They do clean in places that brushes and patches probably couldn't get, and man let me tell you, they do clean. I was pretty amazed when I first used mine, again on AR bolts, the carbon and everything else immediately came bubbling to the top.
If I were you, if you want to try one, and don't need a very big one, go to Harbor Freight and buy the one they sale. It's small but I swear, it works well. It's pretty cheap compared to the likes of the ones with a recognizable name on it. I've been using mine for 2 years now pretty regularly. I've cleaned alot of 5.56 brass with it and can get about 250 empty cases in it.
When cleaning a BCG with baked on carbon its going to loosen some and remove some but you'll still have some scrubbing to do but it will be a lot less, and easier.
I can only see it being worth it if you hate cleaning your guns, which I most definitely do not. I love cleaning my guns, all of them, I dont go crazy on my barrels though, that's a quick way to ruin a good barrel, over cleaning, aggressive cleaning. That's one area where a US cleaner may be better, barrels, put it in and let those little bubbles explode and then just patch it.
Worth it? Try a cheap one and see how you like it. See how it fits into your cleaning regiment, if you dont like it for your firearms they can clean many other things. My wife loves it for her jewelry.