Not sure that anyone has actual numbers, nor do I think it is possible to get anything more than a gut feeling. Are you making a go/no go decision on the purchase based on this info?
In making a comparison you need to decide what with? PAW viz Mk1 eyeball, PAW viz FLARM, PAW viz SkyEcho etc. I am of the opinion that there is nothing close to a properly set up PAW system in giving the best chance of being alerted to a threat. And a bonus is that you can still use the Mk1 eyeball 😄 , in fact you are encouraged it use that first.
OGN coverage east of Tunbridge wells could do with improving to cover Hellfire Corner. If you need to see gliders in this area, start campaigning to get the local airfields onboard, though significantly less gliding seems to happen down where you are.