Yup buy the Daniel Defense Irons for now and save up your money for a real sights...
Love my DD A1.5 rear sight....
Admittedly I have a TRS-25 on my 870, and I think it's keeping it's zero, a little tough when you're shooting bird shot, at least it's all head in the same general direction I'm pointing, lol.... That being said, I think there are 2 things that are being "confused" here when it comes to cheap optics
1) there are cheap optics out there, being made with poor materials and poor workmanship (IMO that includes NCStar, and various other no-name brand optics)
2) there are inexpensive optics that are made with decent to good materials sold for a reasonable price (IMO these includes optics like the Bushnell TRS-25 and the Vortex Strikefire)
Not saying Strikefires are cheap or poorly made, it's that they're fairly wel made, with pretty good materials, for a reasonable price. I think the Strikefire is higher quality than the TRS-25, but I like the TRS-25 physical form better, it mimics the minimalist form factor like the Aimpoint Micros.
However, when it comes to cheap optics many times you can feel it in the quality of the materials while handling them, and cheap parts used.