We've been playing with the EOTech 3x and 4x, and the Aimpoint 3x, here at UltiMAK. They're good pieces, all. For mounts, we tried the regular adjustable EOTech mount (not the flip-to-side model) and the Aimpoint TwistMount with spacer. The EOTech mount aligns the magnifier nicely with the taller 553 model, but it's a bit low for the regular EOTech models, though it's still workable. Oddly, the Aimpoint TwistMount with spacer aligns the Aimpoint magnifier better with the regular EOTech sights (511, 512, 552, et al) than the EOTech mount aligns the EOTech magnifier.
The EOTech 3x has a larger-than-30 mm tube, and the Aimpoint 3x uses a standard 30 mm wide ring, so the mounts are not interchangeable. The EOTech 4x has an integral dovetail, and interfaces directly with the EOTech magnifier bases without a ring. The 4x is a bit heavy, but it's built like a rock and has very nice optics.
The reticles really look nice and sharp through any of the magnifiers. I'd say that if you want a 'convertible' system (1x to magnified) these magnifiers are a good way to go.
If you have the fixed front sight like our RRA, you do notice a ghostly hint of the front sight, but it's not a distraction or a problem at all.
Are they worth the money? I'd say if you had one, you'd certainly not regret it so long as you get the proper alignment. Both the TwistMount and the EOTech magnifier bases are QD, so it's a very easy on/off, and theoretically you could use the same magnifier on several rifles if you have a base on each one. They can also be use alone as a monocular.
We have an RRA M4gery here, so if you're curious about a particular combination I can try it for you and let you know how it goes together. You CAN have it all- 1x sight, magnifier and backup iron sight, without a forend rail, but not all combos work.
