Short answer is, there is no differences . Actually it's very same hardware.
To be clear GLM 2,3 and 4 are the software part where User Kit (8300-601) is the hardware part.
At the time GLM 2 was the latest software. User kit(8300-601) was sold by named GLM 2.0 Kit.
When GLM 3 came out, it was then sold by name GLM 3.0 Kit.
If you have recently bought a GLM 2.0 Kit and wonder if it is latest GLM Kit.
Worry not because you already have latest hardware.
Latest GLM software can be downloaded at link below
Happy listening session!