I have the FP power plus - got it bc it plugs into the wall... i dont have any complaints about it - dont RAVE about it but it does the trick and i have used it with both my boys. I think DS1 grew out of it around 8 months (cant remember exactly). I know i used it a bit also when we first started solids and he was too small to sit in high chair - i used to sit him in there for his solids... so obv it lasted til a bit after 6 months at least...
I dont use it ALL the time but they do like the rocking motion and it is another activity/position for them in these early days...