As long as the client is proprietary, how can one know that they are any better than Dropbox? Feature-wise sync.com looks interesting, but there seem to be ver

As long as the client is proprietary, how can one know that they are any better than Dropbox? Feature-wise sync.com looks interesting, but there seem to be very few users out there. I would be worried that they disappear when they run out of VC money.