I saw quite a few returning/selling those due to personal disappointment, some even after multi attempts to try to get to like it. Any thing is subjective to personal opinion and GBL is certainly no exception.

As for me, I highlighted the benefits GBL offers to a PSR S770 and I've proven my point completely to this effect. It's all about cost versus sound output.

1. If you have no financial constraints, go for the flagships instead.
2. If you feel neglected as a result of current financial constraints, then look at GBL again.

It's just THAT simple really...

One thing I guarrantee, if I had a SX900 I would have:

1. Installed the full GHENOS pack including ALL the Genos Revo & other voices.
2. Installed many more free choir human & other stunning voices.
3. Used GBL & turned a great many standard SX900 styles into versions which could no longer be compared to on-board SX900 styles at all.
4. GBL is a tool - you can either use as is or upgrade a great many styles to your liking with it's powerful editing capabilities.