My parents bought one for my dd, and she loved it! It was fun for her to bake something different each month, and she tried recipes that she definitely wouldn't have tried otherwise. The recipes were very easy to follow (she did them without help), and the results were always pretty good!
It is quite expensive for what it is, and you have to buy any extra fresh ingredients required for the recipe, so it certainly isn't the most cost effective approach, but it's still a nice gift, especially for a young teenager. I don't recall needing to buy any tins/equipment.
DD used to get quite excited when the box arrived each month - there was a lot of fun in the surprise element of "what will I be making this time?" which you obviously wouldn't get if you were just choosing recipes and baking from scratch. It definitely pushed dd to be more adventurous with her bakes, and she really enjoyed that aspect of it.
I wouldn't recommend it for a really experienced baker because they probably wouldn't see the point, but I think a subscription would probably quite good fun for a novice who wants to get into baking a bit more. FWIW, it did build dd's confidence in the kitchen and she carried on trying different recipes afterwards.