HI Sunny, welcome to the site.
I have had 3 successful caponizations so far. 3 out of 3. One that expired was a pullet and she wouldln't give me her testicle - I was on the right side and had I gone in on the left FIRST I could have seen a round pearl instead of, well, nothing, and would have stopped before I did any more damage. Hens' right ovaries are vestigal and disappear before they start even laying.
So, a word of advice I have learned - start on the left and make sure you find a bean shaped white thing, not a pearl shaped white thing.
One of my boys developed a puff - I made a .5 mm by 1 mm hole in the skin with a clean fresh sharp scalpel blade and squeezed the air out - he's fine now. No one had crowed since (2-3 weeks), however, when I put their sisters in their cage with them they did peck the new girls down a bit - but not try to mate. They don't seem to be growing at an abnormally quick pace, kind of like the others are.
I HATE the tools in the Nasco kit - they are useless. My tools include, now, after a lot of trial and error, a 4 inch Weitlaner retractor, blunt ends, a number 3 handle and # 15 scalpel blade (also to open air sac), and my grasper of choice is a jewelry tool - pearl tongs, or bead tongs. They are tongs with a flat rounded top, not a pointed sharp tip. To hold them down, I use bungees around legs and shoulders strung to filled gallon bottles with handles. I can easily adjust the bird without hurting it, the retractor makes the work immeasurably easier, the tongs are small and can go in without hitching on the retractor and being rounded they are not like the triangular sharp ones that tear blood vessels. I also stitch them up, using 3-0 chromic catgut swaged on a reverse cutting needle; two for the intercostal muscles and one for the dermis. I got ALL these things on
eBay or the local hardware store.
GOOD LIGHTING is essential. I also got a coleman headlamp to help me, but it was not as much help as I thought it would be. The testicles are fragile, and the grasping tool is essential. A good, gentle grip and twist the organ out. I found that making the incision directly forward of the point of the hip betwen the last two ribs. When I was doing this alone, I put a towel over the bird's head so he would be calmer.
I don't have any pictures, but a lady may be giving me half a dozen more cocks about 8 weeks old, and perhaps I can make a video of it and pass on what I have learned.
Good luck out there!