what you are doing is gambling. Just like the stock market or gold or anything else.
do what research you can and go from there and hope for the best.
Also, know that for things that bring alot of $$$, someone or someones may decide to do some counterfeiting. it happens sometimes especially where $$$ and greed comes into play.
Whats your endgame too? do you want one for bragging rights? an investment? a toy? If its shot and you shoot it, its not a big deal. Its NOS or really nice, would you want to shoot and and maybe loose some of that value? If you dont care, then do what you want.
But its been said there are better investments out there than guns.
But what i have posted and what has been mentioned before is a thing called "utility". If you are going to invest in things, you may want to research on whats what. but guns have "utility". Gold does too, but its limited. A car has "utility" too. But whats nice about a Gun or car, is that you can use them for other things, such as what they were designed/intended for. Its like having your cake and eating it too. Not many investments can do that. Yes, you can "buy" those things with your investment if you cash out, but if you buy a gun you can play with it too. Just make sure you understand by doing so, you may loose some of its value down the road.
you also need to understand that CZ isnt cranking the short rails out now. i think CZ Custom had some copies made, but they are just copies and not the real McCoy. So there will always be a limited supply of whats out there. Then you need to remember that there are places in the USA where guns are being bought back to get them off the streets. How many CZ short rails will be in there? who knows. But you will have to assume and i do, is that over time, that stock or supply will get less and less.
I bought my guns for fun. And i still do. As far as buying them for "investments' as mentioned, there are better investments. But also as mentioned, i have had my cake and ate it too for each gun i have bought.
I was looking at buying A shortfall for my CZ collection, but for now, its not high on my priority list. I dont have a sample of every CZ made. I dont have a sample of every Colt, S&W or any other brand made. So i know in wont be able to completely make any of my collections complete. So if i dont buy that short rail, its just another of many shoulder shrugs ive done in my life.
If its important to you to buy one for whatever reason, then go for it. Its your money, time, and life. No one can live it for you, but i can spend it for you if you want.
Chances are if you buy one and decide to sell it at a future date, you will probably make some money on it. How much? that will depend on what the market will bare and who wants it. Its not like a Colt where it has a name and everyone knows it so someone may need to do some reserach and learning on what it is. But if you monitor what those short rails have gone for, you may see that they went for some money.