I have recently become the UK distributor for Garsen Putter grips. You can come and test them at my new base North Berwick Golf Club, West Links, East Lothian, Scotland.
Garsen grips are unique as they have a spine down the front of the grip which when installed lines up perfectly with the face of the putter. You grip the putter down the sides and and the “spine” down the centre of the grip allows this to become repeatable. This is quite difficult to explain in words so I have borrowed the words below from Garsen’s website and take a look at their video.