Well Archie I have been asking that same question for a few years now and the only conclusion I can draw is in alot of cases they can be much more cost effective then conventional vitrified stones we have used for years.

I use the example of shops that do not bore to .003-.005 before finished size to hone to size they just use a roughing stone and a selection of other stones to get to size and desired ring finish. 
EG: If you use a EHU 123 stone set to rough out blocks depending on hardness of the block you mat get 4-5 large bore blocks before they are done. Diamonds on the other hand may do 100+ blocks and keep going as long as they do not get crashed which happens from time to time we have all been there but there is a learning curve for finish to go through and a profilometer is a must have item to get it perfect with diamonds.
I have a CV-616 and while there is a diamond setup available from Sunnen for this machine I know guys that use them on a Ck-10 but for roughing only then vitrified to finished size like usual.

Back in the day K-Line sold diamond hone heads for Sunnen and other machines as well as others but there is a difference in stone numbers on the hone head. Some have 4 dual stones some have 6-8 single stone segments.
The coolant is also water based not a bad thing but its subject to developing a fungus like wet surfacers do when not used for a long time and the coolant goes rancid and smells like crap.
Its a good way to update that's for sure but the cost has to be weighed against the conventional honing methods and materials used. A couple shops I know that switched wish they never did because of machine issues in the early stages of their existence with circut boards and like all rottler machines I have seen their customer service can be an issue getting replacement parts in some cases while other shops seem to have not issues with them.

I have been looking into getting a CNC machining center just not made the room for it yet but if you have the extra cash flow to justify the machine and consumables start up costs they are faster and a production shop time is money and speciality finishes they benefit greatly harder then average block and sleeve materials they would be the way to go.

Bottom line is can you support the start up cost for 5 years to see a cost reduction after the machine is paid for.