I've not had any issues with Medexpress and am one of those people who will stick if the price is right - same with car insurance etc 
I just cba with the faff of moving. But is it possible to find existing customer codes? Or is it really a hop around type of thing?
I got my first pen with my blue light discount. Then luckily for me someone used my referral code so I could stick again with Medexpress.