Each service best fits a startup in a different phase of getting to product-market fit. Pick one that has the most value for you, right now.
You need a trained eye to tell you where your UX works and where it fails. Jump in with your product and get extensive notes and to-dos on where to fix the UX. No pitches allowed.
Friction creeps into interactions over time and sometimes you have to whiteboard it all out on a wall to see you core flows in one place and where they're dragging your customer down. Requires facilitation so best done on your premises so the team can use the experience flows as a to-do after the workshop.
For products in the Valley of Tears you have to pull back to the fundamental bets you made on your product features, needs and even users. Invalidating old bets and articulating new more precise ones needs analysis and soul searching but will set you and your co-founder on rails. Best done off-site with only your core team.