I've rented with them several times, in both Europe and the US. Indeed, had a pleasant enough experience with them in Europe that when I started seeing them as an option in some places in the US I happily chose them over the companies I used to rent from here.
Pricewise, excellent (even when tacking on things like additional insurance and such). Their one-way fee is hefty (which is common), so if you're picking it up in Lucerne then be sure that's where you also plan to drop it off. As is common there also, an automatic transmission can sometimes add on a few dollars a day to your rate vs. a manual.
One thing I have noticed about them is they often try and upsell me when picking up my car - I'll rent a basic estate/wagon like a Skoda, and when I get to the desk to pick it up the agent has almost always tried to sell me an upgrade to a nicer car like a Mercedes or Audi. Not sure if they get some kinda commission on this or what, but it's never been heavy-handed or over the top and when I've politely declined they've been entirely ok with that (and, I admit, I've even taken em up on the deal when the car was nice enough!).
So I do think they're entirely worth renting from. As someone who had rented exclusively through Hertz for years, then switched to Sixt after a single experience with them because of how much better their pricing was, I'd say they're a worthwhile option.