I've noticed that quite a few toys come with bullets to give them a vibrating function, as opposed to an integrated motor, especially those from Rocks Off.
Personally I've never got on very well with Rocks Off toys, in part because of their awkward shape, but also because I didn't find the RO-80mm strong enough to be satisfying.
I saw the Butt Boy recently from Rocks Off, and I really like the shape, but the bullet put me off. At the same time I happpened to see the We-Vibe Salsa, which looks to be the same size as an RO-80mm, and it gave me the idea of combining the two.
I'm wondering if anyone else has tried something similar, using a bullet in a toy different to the one which came with it, and what the results were.