They are until they aren't. I deem it not trustworthy for the simple reason that I can't be bothered to look out for any changes down the line.

Startpage should have an option to disable sending the large proxy URLs. These make the Startpage SERP very large (relative to other search engines), especially for anyone who does not need them. Plus Startpage limits to 20 results at a time and requires sending a cookie just to change this basic setting. (Why a cookie. This is supposed to be a privacy focused website. Why not accept the settings as parameters in in the URL or request body.) Finally, Startpage is somewhat quick to block an IP if the user is doing a number of searches in succession. Even if it is a viable privacy solution, IMO Startpage has uneccesarily become too slow and cumbersome to compete.