https://www.firebirdtours.com/

Looking for first or second-hand experience. They have good reviews online from what I've seen but I trust real forum members more LOL.

Considering using them for an anniversary trip to Europe this year (Portugal/Spain)

Follow up. Firebird was amazing and the trip was epic. Highly recommend.

Excellent to hear.
We used Viator in Italy with decent luck, but it's more of a tour aggregator.