hey all, long time listener, first time caller...
I know this is an old thread but I've had lessons with both Kitepower and Kiteboarding Lessons
Depending on what stage you are at I think both approaches (one-on-one vs group lesson) can work.
For sure you will get more time in the water with a one on one from Kitepower. It's also a lot more tiring, especially if you are a newcomer to kiting and learning to water start as you will spend a lot of time and energy floundering around trying to get the board on your feet etc while trying to control the kite at the same time etc. Well I did at least anyway, lol... At the end of my 2 hr one on one lesson i was completely stuffed...

With the KBL / group lesson approach I found it kind of useful to have a turn in the water, then jump out and watch the other person have a go. You can also see the things that they're doing wrong and it helps you to take a step back and visualise how to not make the same mistakes. I would say for a group lesson try not to be in a group of more than 2 students otherwise yeah you will spend most of your time watching instead of doing
I ended up buying a package gear deal through kiteboarding lessons which included a lesson, very happy with the price, gear and the lesson
I also bought a trainer kite from kitepower and got a discount on a lesson, friendly helpful guys as well...
Just my 0.02