I have two AR-15 carbines. One is a 6.8spc and one is a 5.56. They both have a removable handle, a quad rail, a fold down rear sight, an A-frame front sight and a CAA FGA front grip/flashlight holder and on/off switch (great product) with surfire G2L's on them. My level of experience is where I can take them down and clean them as well as do part replacements as needed. My intended use is for home defense or SHTF type of situations should they occur. Given that I would like a couple of top rail mounted red dot or similar optic that is inexpensive and won't break too easily while working out to 100 yards or more. As a side benefit a variable or 2x would be nice. What would you suggest?