I've pretty well use them all over the years and now have the MCCruise (a bit expensive but excellent) on all of my ST1100s on the road.
As was said, are you looking for a throttle lock or a true electronic cruise control?
For throttle locks, Vista Cruise, NEP, Caterpillar O-Ring, and the high priced Break-Away.
For electronic, MCCruise, Audiovox, Rostra.
The challenge with the electronic for a ST1100 is the connection to the throttle pulley.
MCCruise has a CIU (cable interface unit) to deal with it, the other two you have to fab something up (plenty of documentation on the site).
But there is no comparison of a throttle lock to an electronic one if you deal with any elevation changes at all.
Locks are way cheaper and serve their purpose, just depends on your 'frequency' and reasons for use.