I saw a Medicus driver/7 iron together on Craigslist for $75, so I figured what the hoo and bought them (these would've cost over $200 normally). My thoughts on using them effectively:
If you have a fairly serious swing flaw relating to plane, wrist collapse, casting, etc. this will help. It at least allows you to improve these deficiencies. If you're a big time slicer, I think it will really help improve that.
The thing about tempo being disrupted because of the need for a slow backswing - I agree to an extent, but I think I've found an effective way to utilize the Medicus without this being a problem. I'll take about 5 practice swings with the Medicus and then a few practice swings with my actual club before hitting a few balls. If the swing with the actual club doesn't "feel" right in terms of the things I rely on Medicus for, I'll back off and swing a few more with it to jog my muscle memory, then repeat the process. I absolutely don;t advise trying to hit balls with Medicus, though they advertise that you can do this. That will certainly kill your tempo and feel as you try to hit a ball like you normally would with these clunky, collapsing tools.
I don;t know if these clubs have helped me, but my swing has improved a lot in the three months since I've had them. Who knows if they're the reason, but it seems like they've helped. I'd like to see a forum pro comment, as I'm certainly not qualified to act as an expert here. Just my two cents.