I was not sure about which grip extension to get either, but because I was ordering several parts at the same time and could combine the postage I got them both. The desk mounts are adjustable for height and angle, and the extensions are easy to swap in and out so it gives a lot of flexibility.
It only takes a few minutes with a hex driver to switch from a centrally mounted tall stick for helicopters or warbirds, to a side mounted short stick for airbus, or a central mid-length stick for Diamonds etc.
Yes, the OTA referred to is the Omni Throttle Adapter, which puts the grip at an angle and allows you to lock out the roll axis and have a fore and aft moving throttle axis, but retain the twist function and all the buttons. You can get the OTA for either Gladiator or Gunfighter mounting systems, but I personally feel the latter makes for a very expensive throttle, and I don’t really see the advantages over the Gladiator.