I'm writing this as both a seller and buyer. When you upload a design on their site, the colours are extremely different when printed on a t-shirt, because their printing is so low-quality. Why don't other printing services have the same problem? I have bought shirts from literally every other site of that type, like teefury, lookhuman, etc. and none of them have any problems reproducing the colours accurately. It's not a nitpick either, the colours are extremely darker, faded and greyed out. The print is also not opaque on the shirt, so it's even more faded than the preview. I didn't find their white shirt to be particularly good quality, it's kind of sheer. For this low quality, the pricing (30-35$) is outrageous. The other sites I mentioned sell shirts for 15-20$ (6$ for "random designs") and both print and shirt are much, MUCH better quality. Redbubble said they were improving their printing, but that was a while ago and the previews are still just as faded and bad, so I doubt it's any better on the shirts.
The stickers are nice and have nice discounts for them. I haven't bought any other type of item yet.
The customer service when dealing with fraudulent copyright claims is horrid. ALL they will do is send you tired copy-pastes from their FAQ and TOS. They will NOT reply like humans and consider your counter-claims. They don't care who's right, they care about their own comfort only.
Edit: received a shirt recently. The printing and shirt quality has improved. It may be on-par with other companies now, but the price isn't.