My experience with it is that each county has a different "personality", both in the bidding process, how much competition exists, the premium someone's willing to pay (if the county does premium bids, and let's you choose the parcel), whether it's online or in-person, and just the demand on a particular parcel too. From talking to very seasoned TL investors at some of the in-person auctions, it seems that this fluctutates too, based on the economy. The premiums I've paid vary substantially, from next to nothing, to 50% or more on the tiny parcels, but lets say, average 8-10% or so.
So this means you'll likely lose a little money if it gets redeemed the first year (many do). And yes, few actually go to Treasurer's Deed, but, particular parcels have a higher likelihood, if you're willing to do some homework. Once you get a Treasurer's Deed, most title companies consider it a cloud, and won't give title insurance for merchantability. So, you either have to quitclaim it to someone (and disclose this), hold on to it for 9 years, and the cloud disappears by statute, or do a quiet title action on it to clear it.
It's a numbers game, and a game of patience. But worth it if you have the personality for it.
Hope this helps, also, hope I'm not too late, I know most of the auctions are already done this season, but there are 2 more counties on my list this month. Good luck!