It makes a huge difference in the power you feel. Set one (clutch) really high, and you will have a feel for how adjustable they are. I ran a malossi clutch/var for years, and had NO issues at all. I recently switched to Jassil for thee var, and stage 6 mk2 for the clutch, and I can tell you the Jassil did 4-5mph better top end than the malossi. It's five I never had for free.
The clutch I haven't run yet but I already see it is better built than the Malossi Delta, and has much more user friendly tunning. I'd recommend them.