Kegs make an awesome fermenter. The thing about the corny's is that they should be pressurized slightly to insure the vessel is sealed. I use 7.5 gallon Sanke kegs and would never go back to glass carboys. Here are some of the points I picked up over the years fermenting in kegs:
1. Stainless steel doesn't break, nor does it absorb flavors and is a perfect barrier against oxygen ingress. You can add hot liquids to them with little trouble.
2. Depending on your yeast strain, you may need to leave a lot of head room, or you can fill it nearly full with no "puking". Lager strains have very tame krausen, with 34/70 you can fill nearly to the top without much trouble, WLP007 is also tame. 1318 or S04 are both top cropping yeast and have an aggressive krausen during fermentation and you will need a lot of head space in the fermenter. Likewise Kolsch yeasts are big krausen yeast.
US05 is medium krausen, but still needs some head space.
3. You can pressurize them. You can pressure ferment, spund and do pressurized transfers easily. Transferring may require co2, but once you have that, brewing becomes much easier and enjoyable.
4. With a floating pickup, you can ferment, carb, condition and serve in one vessel. When I make a pale ale, I will serve from the fermenter. I don't move it to avoid stirring up gunk from the bottom. I transfer lagers off the yeast into another keg after the beer becomes relatively clear.
Here is a common spunding valve that allows for you to adjust the pressure in the keg during fermentation:
https://www.morebeer.com/products/b...TYKNF5q-OCyvzi9GZiVt8RdCcnFuuQ98aAu5MEALw_wcB
Here is a floating pick up tube you can use instead of the corny pick up tube. This will allow you to draw beer off the top of the keg where the beer is clearer:
https://www.morebeer.com/products/floating-dip-tube-2.html
Good luck and happy brewing!