Correct. But 20 IPC for the tech is less then the 36 IPC for the destroyers. (Assuming you buy 4 rolls and no more.)
Sure, tech can be very expensive and not worth it. That’s part of the gamble. And, if you are facing a 600 IPC army defending Russia (comprised of Russians, English and Americans) and have your own 500 IPC armies (1 for Germany, 1 for Japan) you might want to take the risk on techs to help cut off the flow of reinforcements or bomb IPCs or make your fighters immune to AA fire, whatever since you have no worries about adding to defense, you just don’t have the offense right now.
It’s not something you do on Round 1. It’s something you do when you have time, resources, and position to do it. Or, when you have nothing to lose. For instance, if America just lost it’s transports, stranding men in England and North America, why not roll for Jets? At least those fighters in Russia will defend better this time out.