Thanks to all for the replies.

Joe, it's a very good soundhole pickup, does no damage to the guitar as it does not involve any body cutouts (I have one on my old Guild for that reason)

Many very good guitarists use them (John Renbourne etc). The sound reproduction is terrific.

There are several versions e.g. humbucking, blend, passive etc but I like the active single coil the best. Really easy to fit too. In fact the fitting doesn't have to be permanent if you want to swap between instruments, although I prefer permanent fixing.

Have a listen to one - you may be impressed.

Alex