I have the arrow bertha but just got it put together so I haven't had a chance to use it yet. It was a pain to assemble. It would have been pretty easy if the instructions were any good. The video I found was only a tiny bit of an improvement. The part that goes up and down is very hard to push down so I'm hoping with the weight of my machine (I have the Janome 6600) it will be easier. Right now, with no machine, I can push it to the level where you sew but can't even begin to push it all the way down to the storage level. I kind of wish now that I had invested in one that you don't have to push (if there is such a thing) but since no one local sold these, there was no way for me to try it out. It does have the center needle seating position.
Tomorrow I will try putting my machine in it (we're in the middle of a move and my machine is still at the old house).