After a lot of research and speaking with people who have done the training, I decided that rather than training with a particular brand, I would find a good quality training academy. This isn't usually how I go about training, but I've heard too many horror stories with the pens!
I'm going to train with Cosmetic Couture in Manchester - who are an Aesthetics Training Academy. They use the original Hyaluron Pen. They do a 1 day course for the lips and then an optional second course for the rest of the face which I thought was appealing as many people say that too much info was squashed in to 1 day. I rang them up and quizzed them about the training and they said that they always provide ongoing support and if for any reason I didn't feel confident after the training day, I could repeat the course for free.
I have my training at the end of the month so I'll provide feedback on the course and the pen.
If you want to find therapists using the pen, theres a few Facebook support groups.