My GS is booked in with MCT, who also sorted my last bike (ZZR1400) they really know what they are doing and offer a ride-in / ride-out service.
They can fit whatever you want but tend to prefer Ohlins and Wilburs, they can also modify a lot of OEM shocks and forks, on my ZZR they altered fork springing / damping and re-sprung / revalved the OE shock, although I later found a secondhand Ohlins and fitted that instead.
I like the personal service and setup, before you leave they make sure you are entirely happy, I would say this is well worth looking for wherever you go, especially with very adjustable units which can make trial and error amatuer fiddling a long process.
I did enquire about shock trade-in with FTR, but the problem is if you ever sell the bike you have to let it go with the Ohlins fitted, whereas removing them will get you at least 50% of the cost back, in my case I was offered £200 trade in on GS shocks against £1800 worth of Ohlins.
My ZZR had @ £2.5k of extra's fitted and at trade in time no dealer would offer even £100 more for it like that, I tried private sale with the bike complete and only got offered £5800, pulled all the bits of and sold it at £5300, and then made £1500 selling off the bits.
So for me unless they are offering at least 25% off for a trade in your better off keeping your original units, unless you know you will never sell the bike - and don't forget to tell your insurer as different shock can invalidate insurance.