I would suggest you buy the gun that fits you the best. The 870 and BPS have significantly different dimensions and feel. I have had both and preferred the BPS for the way it fit and swings but that is a matter of personal choice. I have heard of a number of problems with recently manufactured small bore 870s. Another consideration is that 28 ga. hulls are valuable and the BPS is going to eject them at your feet while the 870s will be further away and off to your right. Good luck!
