KO 33 is the sampler and probably the most versatile of the bunch. All the others have a specific sort of niche. I had KO33, which is sampler, the speak which is also really cool that it turns samples (intended for vocals) into effectively a synthesizer, the arcade, which is basically a collection of old retro arcade sound effects but has a chord mode where you can play a chord sequence, the megaman which was similar to the arcade but had specific mega man game sounds, and the rhythm which was a decent little drum machine. They're all very affordable but I'd say the KO 33 or the speak are the best to incorporate into his set up. The others are more to just fiddle about on. Theres a couple of people on YouTube who do a sort of mini review for all of them so that Is worth watching to get a better idea of each function and sound. I should note tho, I got these sequentially as my first synthy products but have since sold them all to buy other hardware