I would say if you already offer gel nails (I'm assuming gel polish only), it might be worth doing a hard gel extension course (as well as your biab extension course). I say this because some biabs aren't strong enough/recommended for longer extensions; biab tends to be recommended for short to medium extensions), but see how you get on with just the biab extension course. More people seem to be swayed more towards gel these days because it is kinder to the natural nail than acrylic, so I don't think you need to offer both gel and acrylic - one form of extensions should suffice x