It's definitely not the lazy man's alternative. It took me a lot of time to get that sucker to fit. It's far from just bolting it on.
Sam James actually recommends rolling your own aluminum baffles to go with it. More work. As Dan mentioned you need a way to seal off the dipstick. Then the plenum inlet rings don't line up with the cowl inlet rings...
Then it's not tall enough in the back so your oil cooler hose will be sucking hot air from between the #6 cylinder fins.
A lot of people who have the James cowling+plenum did it because of installing a high compression engine with a cold air sump, (maybe even ceramic coated Forsling exhaust pipes) which does not fit in the standard cowling. Those engines produce 40+ more hp (depending on who you ask), and a bunch more heat, so you cannot really compare that setup to standard engines with standard baffles.
I have the James cowl+plenum, the bigger cowl intake rings, standard D4A5 engine. I got sucked into it cause I like the look of the round cowl inlets.
I'm in Florida and I don't have heat issues.
My oil temps are in the 180s in cruise, and CHTs in the low 300s. So I don't think it's a downgrade as has been said before but it's definitely a ton more work for just looks...
Lenny