I have one of each of the DSA standard rail type cover, DSA "Para" rail type cover, and the A.R.M.S. "Para" rail type cover. DSA only recently actually delivered the long awaited "Para" cover. Until then, the A.R.M.S. cover was the only practical way to have a rail on a FAL "Para". That's why I had the A.R.M.S. cover. Then, when DSA shipped their new Para rail type cover, I bought one. As good as the A.R.M.S. is, the new DSA is MUCH better. Both of their locked-in-place rail type covers are rock solid and utterly dependable.
I like the A.R.M.S., but any time you can just slide any sight mount into and out of place, the risk of play enters, as does wear of the grooves and grove inserts, exacerbating the situation. Don't forget, recoil has a distinct effect on these components and their engaging/mating surfaces, especially when the weight of the scope, rings, and and bases is considered.
Now that I have DSA's new locked-in-place Para dust cover with machine screwed locking plates, I am much more confidant that the sight will retain zero under any and all conditions. My SA 58 has the similar standard model. Neither has budged in the slightest despite a number of rough field trips and lots of shooting.
Like others here, I cannot grasp why anyone would specifically WANT to have to remove the dust cover, since it's not necessary for cleaning, either routine or detailed. To me, that's like being disappointed because the buttstock and pistol grip don't just slip off.
Are there VALID complaints about the generally superb FAL? Damned straight. But that's a subject for another thread.