Honestly, resistance bands are very suboptimal very gaining muscle beyond the beginner stage.
- They have very little resistance at the start of the range of motion and loads at the end of the range.
- It's very hard to progressively overload. Even if you have different bands, they feel hardly different at the start of the range of motion then a huge jump in difficulty at the end of the range, leading on from the above point. It's far easier to add 2.5kg of extra weight with barbells.
- it's hard to be consistent with the resistance you feel each time because it's highly dependent on how far you stand from the anchor point. So it compounds the point above this one... Hard to progressively overload.
It's not all bad though. They're good for rehab, corrective work, and very unlikely to injure you. Also they're cheap, easy to carry, and better than nothing. I use them myself at the end of my sessions for things like band pull parts and face pulls. So what I'm saying is they're useful, but weights should be the main tool to build muscle and strength.
Also bands don't "tone" as mentioned in some other posts, at least not in the way people mean it. When people say "tone" they mean build a bit of muscle and cut fat. Weights build muscle and do it better than bands. Fat is burned through a calorie deficit. Muscle tonus is something else.