The Magpul Mbus ones are fairly solid and certainly would be the cheapest ones I would ever consider. I prefer Troy battlesights personally. They can be had on the EE for very attractive prices. Magpul MBUS Pros can often be found on sale for attractive prices too. Midwest Industries are also nice, but beware of KRISS take-offs which have short front sights to account for the pistol round's trajectory.
If you want them in the event your optic fails, which is basically never, then the plastic mbus ones will do just fine. If you actually want to use them, then I would say go mbus pro or troy.
I enjoy shooting irons often so there's no reason to cut any corners. The primary difference between the troy and the mbus pros is that the troys lock in the deployed position and require a button to collapse, whereas the mbus pros are closed/open by spring & detent pressure only. They're still solid though.