The downside of these boards is that they will limit you to installing the speaker in the fuel tank area of the frame. This is going to require some serious milling in most circumstances, so it's not going to be as easy as putting a speaker on the top part of the frame on the rear "shelf." And since there is limited depth, in order to get the proper enclosure volume for the speaker, it probably means using a larger enclosure and offsetting the speaker to one side. So what you gain in simplicity with this board on the decoder installation front, you will likely lose on the speaker installation side of things.
Still, I'll be interested to see what engines they fit.
John C.