I have 2 different types of Bassett mounts, and love both of them. Plan on getting a third when I redeploy back to the states. (This one will have 20MOA built into it.)
The low std makes for a very lightweight reliable mount, while the low picitinny provides more adjustment points to gain proper eye relief. I find that both work better if the comb is raised, either with a strap on comb, or a Kydex adjustable comb piece. Since this works well, I do not require the high mounts that allow use of the iron sights as well, because I just remove the mount altogether.
If you follow the directions to the letter, the mount is easy to remove along with the zeroed optic mounted to it, and easy to re-install without loss of zero.
My other favorite is the ARMS #18 old model split rail mount. A very low profile, lightweight, compact, rock solid way of mounting optics. I have found that it is lower in profile than any other mount I have had my hands on, to include the LRB M25 system.
This mount, combined with some decent throwlever rings works well, as there is no way to use the iron sights while the optic is mounted.
Note: Sadlak sells a measure kit so you can find out if your reciever is in spec or not, regarding optics mount options. The ARMS #18 is designed with the M14 service rifle in mind. If your M1A rec dimensions are not to spec, then mounting an ARMS18 may prove challenging.
Be advised that there is a knock off version of an ARMS mount out there. It only resembles the ARMS 18, but doesnt operate the same. Look for an NSN on the mount itself. If it doesnt have one, then it is not an ARMS318 mount.
Hope this helps some.