Sam, both of your talk ideas sound great, I'm happy for you to do either one of them.
I checked out Adhearsion and it looks really interesting. If you could cover the best bits of it in about 20 minutes (we don't like to make them any longer than that really) it could be a good option.
Would you be up for speaking at the meetup in August? There's also a slot at September's meetup available if that's too soon.
Let me know what you think,
Melissa