I use sanke kegs all the time for fermenters. Here's what I do and some tips.
1) Removing the ring and spear really isn't that hard once you do it a few times. Plenty of Youtube videos will show you how.
2) Spray clean best you can. One of those plastic canes with the cap and holes on the bottom you can hook up to your sink works great. Gets most of the solids out just with hot water.
3) PBW or cleaner of your choice soak gets all but the most stubborn residue out.
4) Carboy cleaner (carboycleaner.com) you hook to your drill gets the rest of the job done.
5) Get a small mirror to stick inside and really inspect everything well. A carboy brush should knock out the last bit of residue you may find.
6) Cut the bottom inch or so of the spear off. This helps when racking and leaves behind a bunch of great yeast to harvest.
7) Boil it to sanitize. I put the spear inside the ring and put into the keg when boiling. All that steam sanitizes the spear. Be sure you leave a gap and don't create an explosion!
8) Chill and rack your beer like any other fermenter. Drop the spear in and put the ring back in to seal up.
9) Use any sanke coupler you like for ferment. Just remove the check valve on the gas side, and seal off the liquid side (I use a nickel inside the beer nut but you can buy valves to open/close). Connect line of your choice on gas side and place in sanitizer.
10) ferment. Witness the lovely bubbles in your sanitizer
11) When you're near the end of ferment you can disconnect the coupler, thus bunging the fermenter, thus getting some free CO2 into your beer and I find it helps drive yeast to bottom.
12) Closed transfer! No doubt you can figure out the plumbing (same as tapping a keg, just run liquid to corney keg).
13) Harvest your yeast. Just remove spear and flip the keg over and capture in vessel of your choice. Another nice thing here you can use heat to sanitize the keg opening. I use a small propane torch.
No light issues, no glass breaking, closed transfers, and relatively cheap compared to buying conicals. I've been doing this for years without infection issues. This is no different then learning anything else about your system - you figure out how to clean and inspect properly and will gain confidence as you go.
If you need photos I can find time to provide what you want.