The AviGround unit is similar to other trolleys in years gone by, they are very difficult to line up on the skid tubes correctly.
I'd stick with the chopper spotter as it has the arms that can be moved in and out if you don't the the unit absolutely perfectly in place. They;re not a perfect solution but pretty good. Can't comment on it for the 429 but the company I work for uses it on a B427 easily enough.
There is another trolley out there that I have seen that has massive rubber blocks that the skid tubes sit on when the lifter is raised hydraulically. This makes it quicker and easier to line up (doesn't have to be perfectly lined up like the aviground unit). I can't remember who built this one though.