Hey Eddie a question for ya

Belt driven or coupler. What do you think is more reliable and efficient? Did you see more coupler issues that belt replacements in the shop? I would imagine belts need to be changed more often than couplers.

Coupler or belts. Lets start with belts
Most times belts cost less
There quicker to change if one breaks on a job, because if your lucky you can walk one on like a bike chain and get back to work.
Belts will slip most times before breaking depending on the problem.

Coulpers cost more.
Take longer to change. Most times in the shop over an hour.
They allow for direct drive and take up less space (No off set for belt adjustment)
They don't need adjustment and don't slip.
If you break one most times your going back home to to the shop to repair it.
If you happen to have a unit with a pulley and belt on the same shaft with the coupler keep a extra belt tied to the blower in case the other breaks you can just install the belt and get back to work.
I have seen belts with proper adjustment and servicing of the unit last several hundred hours, the same goes for couplers  
Here again it's about balance, to much vac. pressure increases the load on the coupler/belt. Increased load makes more heat from the engine and blower.
Lets face it the manufactures of this equipment build them to meet their requirment with very little over kill why, because of money.

They know the life of the parts and then you have to repair it.

Look at a Boxxer 421 it has a coupler with rubber plugs factory says remove the old ones clean and install new plugs. think about it rubber and metal guess which wins. On this type of coupler I apply super lube to the plugs and they last longer.
Don,t over tighten your belts they are supposed to have a little give 

even a coupler has give you just can't see it.
One last thing do not confuse a poly chain like what a HM direct drive 4.8 uses on the blower drive it should be tight they won't give like a belt they break. Hope this answers the question didn't mean to be long winded. As you can see both have their pros and cons  

I have worked with a lot of units and I prefer belts for all of the reasons above. Couplers can put u out of work for the day and belts don't. As an added bonus it gives you the ability to make changes to sheave sizes to fine tune speed of the components if you ever so desire.

Not winded at all Eric I enjoy reading your responses to these questions.

I'm with you Fuzz for all the reasons you mentioned