N.B.: I speak only of the 14" version HP9-1. I haven't used the 18.5" version.
Cons
It uses the late-style magazine spring retainer.
It requires modification to employ a magazine extension.
It does not have the Flexi-tab components.
The bead thread is non-standard.
It cannot enter the USA. Ever.
Snobs may shun you.
Pros
The quality is very good.
The finish is better than the Remington Express versions.
Most 870 parts fit.
The 14" version is widely available.
The price is right.
Snobs may shun you.
Put a mag extension on mine with no mods at all...
+1 on what he saidThe modification, to which we referred, is for those late-model magazine spring retainer detents in the magazine tube. These detents should be removed. (A reamer works nicely.)
These detents, if not removed, may interfere with the movement of either spring or shell through the magazine tube at this intrusive high point.
Or...you can just take your chances.