Blue Jays, in over 40 years of shooting 870s both personally and professionally, I've seen only a few Failures to Feed.Most of those were caused by short stroking or baby stroking the slide. If one uses a fair amount of effort, the 870 WILL feed.
The 870 is quite reliable.
As for extended mag tubes, there's a coupla minor advantages besides a few more shots before reloading. The extra weight removes some bite from the recoil and when using slugs,acts to stiffen the bbl and reduces group size, oft considerably.