I've seen multiple assessments of the Archer, ranging from "complete joke" to "quite useful in its designed role". Viewed as a straight-up replacement for a towed anti-tank gun, it has a number of obvious advantages, the only real downside being that it's harder to hide. Viewed as a tank-destroyer in the M10/ Marder/SU-76 mould, it has a really obvious problem.
I take the word of the users over that of casual observers. The RA users of the Archer were quite happy with it. They kept it until the 1950s IIRC. Sure, the rear facing gun was not the best but it got the job done.