From what was explained to us, the implants are sometimes used in aggressive drakes or ganders in attempt to suppress testosterone and curb aggression  In our case with Ritz, we tried it to attempt to shrink the testicals to give some relief and "reduce the pinch" of the nerve. Unfortunately, it had minimal effect but he WAS very sweet in his final days.  Not sure it had anything to do with the implant. I am by no means an expert on this subject matter and I am unaware if they have any effect on tumor growth rate.  That might be a better question for a veterinary professional.
I'm not sure it would have been worth it with Cheeze since he was very sweet and not at all aggressive.  We suspect he went sterle about a year or so prior since when we did try to incubate in attempt to get baby Cheezes, all three batches turned out to be duds. We also speculate that he had his tumors start to develop about the same time as Ritz, but his grew into his abdomen rather than into the spinal area.  It is also possible that Ritz's were more Renal in nature. The sizes of these testicle tumors were truly crazy and if stomachs are OK with it, i can post photos.  They aren't TOO graphic, but just a warning.  Still, what are the chances of 2 unrelated drakes having testicular related tumors???  We sometime wonder if they might actually would have been brothers.  Ritz sure was the "Pretty guy'."