I've used AutoSlash every year since i first learned about it. Each time was effortless, and over the years AutoSlash has saved me hundred$ of dollar$.
Mind you, each rental was domestic: i will try Autoslash in Europe when quarantine restrictions allow Americans back. And i'm a very basic and undemanding traveler who's learned that a teeny bit of flexibility is rewarded with outstanding customer service.
Several years ago I had a bad accident with an AutoSlash car, and the AutoSlash person i reported to was extremely helpful. Since then i've always opted to get car rental insurance (Allianz is my favorite provider). Since i save so much $$ with AutoSlash i'm happy to pay a little more for insurance.
I've tried to convince friends to use AutoSlash, but they're boomer little old ladies who can't wrap their heads around the e-mail business model. As a boomer little old lady myself i find AutoSlash's methods to work just fine.
If you can love a company i love AutoSlash, and i don't know why more people don't know about it. AutoSlash still seems to be a best-kept secret of sorts.