We are 100% P&L based (so not even RVU, what you actually bring in...). There is a small practice tax taken out to compensate admin time for those doing it, and there is also a night stipend/tax for those doing more/less nights than average.
I strongly prefer it. With multiple caveats--
(1) The books need to be open so you see what the hell is going on under the dash. Some CMG giving you a pure RVU pay scale, then taking 30% of your earnings for themselves would be... suboptimal.
(2) Scheduling needs to be equitable, since volume and reimbursement can be different during different times and days-of-week.
(3) You need a strong QI system, and a group ethos that while speed is VERY important, quality, safe care is the MOST important.
(4) People are going to be aggressive picking up charts and cases. Cherry picking of, say, insured patients is NEVER ALLOWED. Period. Cherry picking an easy-to-dispo case because your shifts ends in 30 minutes is just logical. But you need to be able to play nice with your partners when it is slow, and go every-other and talk through any issues.
I would not worry about "not being paid for slow shifts" if you are going to be full-time at a place long-term. Things will average out. IF you are doing a 144 shifts a year (12x12) it is very unlikely you are going to have significantly more slow shifts than your partners.
The benefit is you actually get paid for the work you do! The benefit is if you get the automatic bonus if you get the crap beat out of you x 10 hours... you are getting paid more! The benefit is if you are getting slammed, and the overnight doc asks you to pick up a few extra charts... no problem, you'll get paid! The benefit is YOUR personal charting, YOUR ability to properly write procedure notes, YOUR ability to bill for critical care time comes right back to YOU! The benefit is if you bust your butt, and see 2pt/hr and rapidly dictate and don't doddle and chat during work... you'll make more money than the person seeing 1.7/hr. And you'll see there is just a general philosophical bent (call it capitalism) for your shop to be lean and fast and get things through.... it'll be VERY rare for you to show up and have the outgoing doc sitting on the edge of his chair with his coat on, and 10 charts in the rack.
But if can, like all good things, be perverted either into a scheme to keep your money away from you (some CMGs) or allow unscrupulous physicians to cherry pick and be bad partners.