I like mine, built it myself. It’s just got side-to-side motion. Seems to improve comfort on long trainer rides, I’ve a few 5-6h rides and the ones after the rocker were definitely more comfortable. I don’t do a lot of racing or sprinting so I don’t feel like I’m missing much with the fore-aft motion. I could add it by building another layer for this one.
I used a scrap piece of finished fibreboard that works and was free. The 5" balls and five vibration isolation mounts weren’t terribly expensive, picked up countersunk 3/8" bolts from Spaenaur, and a couple of m10 bolts to mount the trainer. Also need to pick up the right size bit to countersink the bolts, I think I just used a 3/4" but don’t recall the size off hand.
So the balls go under each side of trainer, and the vibration isolation mounts provide the tilting motion. I also bolted my kicker direcly to the plate by swapping out the bolts holding the legs on. Mine is based of the lifeline rocker without the holes for the balls, just had to fiddle with them to get the air hole pointing the right way.
If I were to build another one I’d use 3/4" plywood for the base as the HDF does bow up if the balls are inflated beyond a few psi, but I prefer to keep them soft for more ‘wobble’. I didn’t have to finish my HDF so that’d add some cost, though skateboard grip tape seems common on commercial plates. I had a ball inflation gauge already but it’s not necessary. A level is handy if your training room has a level floor. Seen a few plates with a little bubble level attached. I’d probably spring for stainless bolts on the top of the deck since the flack ones can rust a bit due to sweat, but it’s usually really dry in the winter so they aren’t showing much rust despite going on 2 years. Easy enough to paint them too.