The only criticism I think is from the frame that goes under the mattress. Composed of tubes, it inevitably distorts the mattress from below, which is not too bad if it is thick enough (18 cm for us). I fear, however, that on thinner mattress, it can be annoying and denting the child. Moreover, this frame is retained by the weight of the mattress, so if your child likes to play around feet, it could very well remove the barrier easily. It is possible therefore to use the D system to hang the frame to the bed with straps.
In any case, it's a purchase I recommend :)