I was a member for seven consecutive seasons together with a group of friends, until the 2012-2013 season I think. We joined because it seemed to offer great shooting opportunities within reach of London at an affordable cost, and just because we all wanted to get into wildfowling. It did not disappoint. Yes you have to book in advance and do bag returns, even back then it was mostly online, I suspect you can do all of it online now. But then it's like any mostly volunteer organisation: you need to put in to get the best from it. There were a lot of blanks, a lot of very short nights, a lot of frustrating outings. We were severely limited by having no dogs so we'd have to pass on shooting opportunities (and they were rare). Also we had to plan our trips in advance looking for overlaps in our personal availability, suitable tides, moonlight, and wildfowl don't care about our diaries. Also, your hunting territory is essentially the sky and the North Sea and you need to somehow be within 40m of a duck in that vast landscape, then not miss when it happens.
There are also some inland marshes that are easier, some roughshooting leases in woods which is where I realised that since I was stalking woodcock and rabbits on my own anyway and kept coming across deer, I may as well do that instead.
The reality is that when you're not local, you can't make the best if the natural opportunities. But I don't regret those times at all. One of my friends recently moved to a village in Gloucestershire. We went for a walk this weekend and came across a marsh with the local club's sign. It's taken a decade, children etc, but now it turns out the marsh is ten minutes walk from his house, he'll be back out there ASAP, which wouldn't have happened without the KWCA experience.