I disagree with the last comment. The Prostaff may be better I can't comment because I haven't used one. However, I've used two Simmons scopes as well as had 2 Leupold VX-I's which are a step above the Rifleman line. The Simmons have held up better and longer. Both Leupolds I had to send in for repair for failing to hold zero after some use.
During daylight I couldn't tell a difference between the clarity of the Simmons, a cheap Tasco I've tried, or the Leupold. They all looked fine but I didn't see one being better than the other. I don't need good low light performance as it's not legal to hunt here at night. However, just for the heck of it I did decide to compare them at night to see how they looked. Now I can't do a professional test or anything so it's just what looked clearer to me. I used a Leupold 3x9x40, a Leupold 2x7x33, a Simmons 3x9x40, and a Simmons 3x9x32. I looked down the hallway of the house at night at a red led on the phone base. With both I could see more with my eye than I could see through the scopes. With the Leupolds I could see the red led but that was it. I couldn't really see anything around it. The 3x9x40mm was slightly better but it still wasn't much better. With both of the Simmons I could not only see the LED but I could see the wall and phone charger where it was slightly lit by the LED. I could see this with my naked eye too, it's just that I couldn't see it through the Leupold scope.
To top that off while mentioning I've had both Leupolds repaired I've never had either of the Simmons fail on me.
Now while I do say that and will say I don't see the advantage to the Leupolds at all at least not these low end Leupolds, there are other scopes in the same price range that will blow the Simmons and Leupolds out of the water in clarity both in daylight and low light.
If you can spend $200 or so the Burris Fullfield II is a great option, the Vortex Diamondback also seems to be a great option, as does the Nikon Team Primo's. Then for slightly more you can get a Bushnell Elite 4200. All of those scopes make the Simmons, Tasco's, and low end Leupolds look like pure crap and will make you appreciate a good scope. I would probably go with one of those if I was going to spend $2-300. However, if I only had $50-80 I think the Simmons are a decent choice for the price and certainly better than open sights in most cases. I would also buy a Simmons before I would buy another Leupold VX-I or even a Leupold Rifleman. Unless I got an amazing deal like I did on the second VX-I I bought.
Another issue I did see with one of the Simmons I've used is the adjustment was marked as one click equaling 1/4" at 100 yards of movement. I moved it two clicks and it moved at least an inch if not 1.5" at 100 yards. So the clicks didn't seem to be as they were labeled. The other Simmons doesn't seem to have this issue or if it does it's no where near as noticeable. I've also used a Tasco that seemed to adjust as marked. It was just that one Simmons that didn't and it may have just been a fluke or something. I turned it two clicks. Saw where it shot and turned it back one click and started hitting dead center so never adjusted it again. It was already sighted in very closely before I shot it. This does seem to be one of the things you give up in a cheap scope from some of what I've read. However, once getting it adjusted they seem to stay zero. So as long as you are like most hunters and set your scope and leave it you should be fine. If you plan to be adjusting it often you probably should spend more.
That being said I've never gotten the friction adjustments to adjust like I want them to on the Leupold VX-I line either. In fact I think they are the crappiest adjustments I've ever used so I can't say it's any better at all imo.
Now this is all my opinion and I've not performed any professional tests. However, I suspect that most that have used both will agree with me. I know a friend that's the best shot I know has a Simmons on one of his rifles he loves and sold me my second Leupold VX-I because he didn't like it.
Another friend that is a pretty good shot and used to do a lot of shooting but now mostly just hunts also doesn't use Leupolds. He had an issue with one and since then has had the opinion you are just paying for the name which I think is mostly true. He has several Simmons as well as many others.
I read so much bad about Simmons online but 98% of the people I know locally use them and I only know of one that has had one fail. I know of 3 people who have had Leupolds fail and I only know of 4 that own them. I've also got several friends that have had great luck with the Bushnell Banners. I know a couple guys that like Tasco's but I know several others that don't like them at all and have had issues. Overall, I read online how crappy cheap scopes are but in the real world I don't seem them failing as often as I read about online.
BSA is the one brand that almost everyone I know that's tried one has had issues. It seems to be a cheap scope to avoid. I figure when the guys I know that like Tasco's and Simmons all have had bad experiences with BSA's and think they suck it's probably a good idea to stay away from them since they clearly aren't that picky.
I think we can all agree though it's no Burris, Bushnell Elite, Nikon, or similar but for the price they seem to function okay in most cases at least the ones I've seen have.