Saw you posted at SR, but I'll give you details here. You mentioned SP there, so I'll include it here.
SP's and OH's have been out a long time and they have a lot of fans. Nothing wrong with them, other than the gas part.
For me, they all three have companies that stand behind them.
If you ask owners of each, they'll tell you. I haven't looked lately, but I don't remember an OH or SP thread, that tells me something.
As you can't go the gas route (I believe you said that wasn't an option) then you need to compare them burning only wood.
They're all rotisserie units so it's hard to compare.
I'd look at internal layout (racks, how much space, etc)
You can run the OH/SP on just wood but you will have a lot of ash to deal with. I don't think they're primary purpose is wood only and in some restaurants that run that way, no gas, I believe ash removal has been a pain.
Because the FE burns more cleanly, it's been marketed as a "less ash" alternative to all wood.
Product produced?
I'll give you a story from a professional who used only stick burners before. He competed and won a lot. When he opened his restaurant, he went with CS 500. He said that it was the best pork and brisket he ever cooked and his customers love it. He also said he wished he could turn results like that in at the contest he loved it so much.
It's hard to tell without talking to other owners, so many some of the pros can come in and tell you their stories too.
You might want to call CS and ask John Shiflet (sales) if he knows of any owners in your area so you can see/taste the specific products.
Russ