Thanks Redtail. I've looked at the Victron and agree with you it's probably the way to go as it has Bluetooth as well. Where do you mount it? The pocket on my panels that houses the existing PWM is too small for the new controller so it would have to "flap in the breeze"
Interestingly, these guys 
Attention Required! | Cloudflare are promoting their "KickAss" brand (stupid name) and I know it's just a generic Chinese unit re-badged but is affordable and would accommodate an upgrade of battery setup to lithium in the future.