I have never seen a shop that rents BP/W's as standard rental gear. Not that it's not a good idea.
I wonder about the expense vs. a basic BC with weight belt though.
I typically see Sherwood and Scubapro gear for rent - Sherwood Brut's seem pretty indestructible.
I'd recommend your friend look at the material the BC's are made of also. Some models (Zeagle is one) are made of Ballistic Nylon, it will take a lot more abuse.
I don't know if beanojones is still around but afaik he was doing something similar recently.
If your friend stocks open-heel fins, he'll sell more boots. Plus if he's in Ireland do they even wear full-foot fins in cold water?
At least here, the standard process is you purchase yoru personal mask/fins/snorkel before class. It's probably a good revenue stream for a diveop since it can be upsold easily: "you're going to continue diving after class right? Better to buy the good stuff now..."