I think it makes most of us sad but I definitely think it is the best decision to let him leave. He wants guaranteed first place which is not something that we can offer, not when we paid > £30mil for Leno and pay him the salary that he gets. That apart from the fact that he has been very good in goal for us for probably 99% of the games.
I think we all wanna see Martinez play and he deserves a chance to be undisputed no 1 at a decent team.
Cash in around £20mil on him having not spend even £5mil during his whole career is a good piece of business. If we can spend £10mil on another decent keeper (Raya from Brentford as per speculations or another decent 22-23 years old) and use the remaining funds on a possible transfer in the midfield, I think we can declare ourselves happy.