Be careful of where you read. Axminster's description for example is misleading.
I looked into this recently and though I didn't buy the tool, I checked the Bosch website and the two modes offered by the GEX 150 turbo are
Random orbit - orbital sanding including a secondary random orbit which is affected by friction from the pad on the surface - press harder and the random slows down, ease up and the random orbiting speeds up and leaves a finish with a less regular pattern of scratches.
Gear driven - orbital sanding plus a fixed, gear driven secondary motion - the videos show that this mode is much more efficient than a simple orbit or a random orbit for fast stock removal.
Basically the GEX150 turbo is an alternative to the Festool Rotex and Makita have an equivalent tool. The gear driven secondary rotation is what pushes the price up.
What I think you asked for is a machine that has the simple orbital action of some finishing sanders plus the ability to switch in a secondary (random) orbit. That's different from what the GEX150 turbo offers but it may be what the non turbo model does.
I should say that I went the cheapskate route in the end and bought the metabo SXE450. This is a random orbit only machine, but you can change the radius of the secondary (random) orbit between two values (one for rough one for finish). I decided that sander was good value, well built for the money and the traditional shape suits work on horizontal surfaces. It's vibration is a little higher than I'd like but it's Ok and it costs quite a lot more to get lower vibration.
