I was looking at one of those a number of years ago, did a bunch of reading online about it. There did seem to be a number of issues that were commonly encountered by owners, stuff I never would have thought of, like the "oil leak" mentioned above.
The gun had a definite air of "neither fish nor fowl". It has the look, the bulk and the weight of a recoilless rifle like the FWB300 series...but it's not entirely recoilless. It fires at a low fps, I believe something like 600fps, which is preferred for target shooting but very low for most other purposes, and yet it still requires a PAL to purchase. In the end, the info I found steered me away from buying the gun.
I'd suggest doing a lot of research before committing.