Used Etsy On Sale last month for the first time, just to try it out. I like the look of the regular price with the slash through it to show the savings up front to the potential buyer. The sale name (Cyber Monday Etsy, Columbus Day Sale, etc.) can be added to every item description or just certain sections of your shop with no work by you. Adding or deleting all those tags is so easy with EOS, so for you, it saves a lot of time. I think EOS is simpler for the buyer too - they don't have to remember or write down your code to add during check out. No figuring in your head (30% off is HOW much?...let me get my calculator, then I'll decide if I want to buy it).
This is our first Black Friday - Cyber Monday to use Etsy on Sale. We used the coupon codes last year. So far sales are the same year over year, but we still have more than half the day to go.
If anyone wants a referral code for EOS to get 5 free credits, convo me. I'm all for keeping it easy, so for that reason alone, I give it a thumbs up.