The problem with that for mtb is that you’ll still have problems clashing as you’ll have bars hitting. You can’t have them end to end as you couldn’t hang a bike off the back wheel it would have to hang from the fork mount and you can’t adjust those unless you had multiple bars to attach to.
What you really want is a north shore rack, google that they are fantastic. Don’t think you can get them in the uk though.
TBF the genuine one isn’t that bad for 3 bikes as long as you keep a bit of pipe lagging for rub points. I find it a lot easier than some tow bar racks others have and it’s on there and it’s tucked away when not in use. 4th bar is nigh on useless though and the thing is eye wateringly expensive…