I swear varlinks have been broken for years - only ever got them to work consistently for half a year or so. There are better ways of doing what varlinks do, and don't require the client to have them.
I'm not sure about the slowness because every time I got them to work, they'd trigger immediately. May just be an issue with your server. As for why the clien needs VCE, varlinks are links in themselves, they just go throug a process to convert the action of clicking a link into activating a varlink. Therefore, if this process is done on the client's side and not the server's side, anyone clicking on a varlink would essentially be clicking a link to a webpage, because that process cannot be carried out. I've never looked at the code to see if this is how it is done, it's just my best guess. There isn't really a reason in knowing why the client needs VCE for varlinks, just use another method. They are also hideous if you don't want cyan, underlined words everywhere.
