The down side is that you never know when they're going to call your name. I suspect that's why they have such a high rate of people saying "no," it's one thing to have saved $1,250 for a gun, it's another to have $1,250 saved for a gun that you can successfully keep sitting there waiting for your call anywhere up to two years after you put the money away. But, the small investment (cost of GCA membership, $5 for the notary stamp, and $10 to ship it), was worth it to be on the list and have the option.
Yep, generally the timing is not known. I did not follow Round 1, but I think the Random Generated Numbers, RGN's, were, in fact, randomly assigned. The CMP probably didn't know how many people would apply and how many pistols would be transferred. If that was the case (an assumption on my part) this meant, at the time they assigned RGN's, high RGN's might not have received a pistol.
With Round 2, at the time the RGN's were assigned, after all applications were in at the deadline, the CMP likely had enough pistols transferred that they knew they could fulfill all applicants. Really no need to assign RGN's "randomly" since pistol condition is really a factor of the crate that they process at the time an applicant is called. The only advantage of random numbers would be early numbers get theirs first. I procrastinated, and I waited a long time. Super happy with what I got, and I was OK with the wait.
So, how to know, or approximate when the CMP will call... On the CMP 1911 forum, people were reporting their RGN's and when they got the call. People also reported what their RGN's were, and they were able to get an idea what the starting RGN was, i.e. the lowest member reported RGN was, say 20,054. The highest reported RGN in Round 1 was in the 19,000 range. It was inferred then that the starting RGN for Round 2 was 20,000. Knowing that, and tracking when specific RGN's were called, you could project to an approximate date when you would get the call. There was a member of the CMP 1911 forum that was doing this, then they stopped, so I started my own tracking for Round 2. I tracked working days, not calendar days.
Easy way to ballpark wait time is CMP was processing about 34 applications per working day. So, (Your RGN - Starting RGN) / 34 = working days before you get called. Plug that into an online working day calculator to get the approximate date. Have money ready on that date. The number the CMP processed per day varied to as low as 24 per day, due to holidays, season, etc. so as it got closer to my number, I tracked it closer.