I am a recent convert to the floating donut, and I would highly recommend it.
Last year I was reluctant to start one given it took a potentially cash-making rookie out, and left me with less cover early on. I traded in the WC D-M FD option (I can't remember his name) around the byes though. That was a wasted trade because I rarely seemed to have the right number of playing players on either of his lines - ie, I was left with no cover, or had other options I could use as non-floating donuts.
This year has been very different. Uebergang has been extremely useful, particularly because he is paired up with Adams, Brown and Tippa. Adams has been consistently solid but the others have been up and down, so Ueber has worked well to either loop the Ess options, or to switch up and back with Adams to take the better of D7 and F7, sometimes knowing exactly what both of those scores were (no guessing).
Petracca has also been useful as another option, particularly for the C loophole, given sometimes you can't do forward, back and C loopholes with just one agent. He will presumably be generating cash in a month or so, which I will welcome, but I may even consider another FD in his place, especially if the downgrade options get thin.
The other thing that has made it very worthwhile this year is that the top-flight rookies have been excellent, but the last-selected ones have all been pretty underwhelming in my view - so I haven't really foregone much, but I have still had a strong chance at boosting my score every week. It's obviously useful for trades as well.