Everyone has different ideas about springs, and when they ought to be replaced. Especially the people who sell springs.
That being the case, I would point out the US ARMY standard for the 1911A1 spring was length. Not cycles, round count, or any other measure beyond the standard bent(kinked), broken, rusted, cracked, torn, burnt, etc. Without visible physical damage the serviceability of the recoil spring was determined by its length.
I don't have the TM handy that I used in the 70s, but I do clearly remember that shorter than the specified length was unserviceable, (even if it worked fine..) and would be replaced.
I'm fairly confident that is also the case with the 9mm Beretta pistol in service now, though I can't say so from personal experience.
What can a spring tester tell you?? How many pounds it takes to compress the spring a given distance. Useful information, if you can compare it to the specs called for. But, does it have a practical value?
What I mean is, (first we assume the tester is correctly calibrated) what do you do with the information? If its supposed to be an "18lb spring" and the tester shows its really a 17lb spring, do you replace it?? Is it needful to replace it? What if it tests 12lbs but works flawlessly??
What ever compression weight measurement the spring is spec'd to be, WILL be well above what is needed to run the slide. So if you test your springs against "book value", when things differ, what do you do?
At the least, you'll have to make a choice you never would have had to make if you hadn't spent $40 on a spring tester!