I can't think of a better tank for a lone male than the Fluval Edge. They seem to be perfectly designed for them! When aquascaped properly there is nothing better!
Isn't access to surface oxygen limited to that bit in the middle though? I'm sure this is enough but as Bettas need to be able to breathe at the surface I personally would go for a tank that allows this all across the surface rather than one area.
Been looking around for a tank of that size for a betta male, the arcadia arc dosnt appear to be suitable for my house as i have cats and cant see it has a lid, which if it dosnt its a definate no no to that one. wouuldnt the fish go to the space where it would be able to get to the surface, or would a 30L Biorb be more suitable.
I've just introduced a lone male betta to my Fluval Edge and it seems ideal - with the single exception that you leave a little space free at the top so they can access the surface. The little gap in the middle wasn't enough, especially as that's where the filter output is and he didn't like swimming in the current to get to the air.
In fact it's ideal that way as I've read that bettas like to breathe warm and humid air, which is provided perfectly by the Edge.
As others have said, another good option is the Arc tank (it does have a clear plastic lid!). Avoid Biorbs if possible, they're hard to retrofit with your own gear if needed at a later date and the filtration system is not ideal. If you have a store called 'The Range' near you they also stock a lot of small, 20-60l all in one tanks that would be ideal for bettas.
Just noticed that you're in Shropshire, it's probably the same shop I go to, lol! It's mostly household tat but the fish section is surprisingly well stocked, good for cheap heaters and water conditioner too.