I'm looking for a red dot sight for my M&P15A. I don't want to spend half of what the gun is worth on an optic. And I'm not going into battle. I was hoping on something that I could have had the option of magnification as well but I haven't found anything under $300. I've found a Bushnell 1x28 Trophy Red Dot for under $100 and it looks like it is good quality. Any experience with these?