Comes up often on the tomato forum and the reports on them are excellent.

You wouldn't be able to use any solid fabric anyway and it isn't as if there are snow storms of pollen. The tulle has proven to be more than adequate with the few vegetables that aren't already self-pollinating..

The only issue might be the size of the pre-made bags if using them on extra large blooms such as squash blossoms. And of course you can always isolate varieties by timed planting, hand pollinating, or by successive crop planting of different varieties.

What specific vegetables are you concerned with?

Dave

Here is a link that might be useful: Bagging Blooms FAQ