Never tried them - but for a triple driver, they seem to be good value for money. Whether they will be as good in terms of headroom as something like a ZS10, I'd probably question that. They (the GR i6) will probably will sound better (assuming that they have been designed properly)... so it's going to be a trade off between headroom and heading towards a nicer tuned IEM... but there's not a great deal to go on in terms of reviews or my experience with them. The only thing that I can find, is that the drivers are 2x bass, 1x treble (as opposed to a bass, mid, treble) so you may get the headroom in the low but you may end up with an inherently smiley face EQ - but that can actually be very pleasant for bass, depending upon the style of music you play.
If you were happy with an E2C, I suspect you will notice an improvement as the i6 should give you a better low end response. I would be interested in the driver type in there - if they are dual dynamics and single balanced armature, they could be really good fun, as they would follow the same sort of design as the UE6... which are an immense IEM for bass players. Im a bit disappointed in the lack of info on the GR Bass IEMS to be honest - there's pretty much nothing out there about the specs. GR Bass aren't going to be taken that seriously in the IEM market unless they start divulging that kind of information.
If you can get a good deal on them, they are probably worth a punt. They look decently made and comfortable enough.