I use a buggyboard on a powertrack. Fitting it is no problem (as long as it is a "new style" one - ie not a secondhand one from a couple of years ago). You have to be careful where you put the connectors so the pram still folds up properly (not difficult as long as you think about that aspect).
The problem is that there might not be enough height room for you toddler. No problem with the matrix carrycot thing on. But when the pram seat is on, we have to take the hood off. The back loop of metal on the hood is just where dd's head needs to be. But the raincover fits without the hood so thats ok.
Also you can't recline the seat fully when the toddler is on the board. Only about halfway.
Its horrible to steer with the board on, but I think that is just because it is so nice to push normally!
I've been using it for a year now and the frame hasn't buckled yet...
Dd also sometimes sits on the footplate over the front wheel, facing backwards with her feet in the shopping basket. Only on level ground though as that does make the pram a bit unstable.
I also have a feeling that in 6 months time ds will want a go on the board and dd will reclaim the seat...