From what I have seen and heard GC tanks are usually built quite sturdily, with thick glass and plenty of bracing where it counts. The silicone can be a bit sloppy at times, and I have heard of a couple of stories where people got tanks built and didn't / weren't advised to, give the silicone adequate cure time leading to seam failures.
I would definitely consider a GC tank given the pricepoint, just be aware that the silicone needs to cure for weeks (not days). If you want absolute aesthetic perfection, then go with Miracles or another builder but expect to pay a LOT more for a similar sized tank.