I agree. A HTML5 implementation would be so much more compatible. Realistically people can only use Web Client Pro within Internet Explorer but there is also a bug in the latest Java which stops Web Client Pro from working even in IE.
Are you having the same problem? I have raised a ticket and also posted it here..
We are currently evaluating all options how to remove dependency on Java with aim to add the most effective solution to Serv-U roadmap soon and update for Web Client / Web Client Pro is one option. I will give an update on Serv-U THWACK once decided.