I use the sanke kegs .... and while the cleaning and filling is a LITTLE more difficult, not really that much. An I prefer the tapping approachh like sanke does. You CAN open them, but I find that unnecessary. I have always cleaned, sanitized and filled right through the sanke tap.
There are videos to show how to remove the retaining ring to gain access to the "stem" but I opened one a week or two ago that I had been using for YEARS ..... and saw absolutely no grime/sediment/debris to cause any worry. Now that may be different if you dry hop right in the keg - or other methods like that - but I am just going to leave things be - since it works for me!
BY THE WAY, I DO make sure that the empty keg either sits in the kegerator (mine holds 3) until I am ready to flush and fill - or I clean and sanitize right after removal from the cold environment.
My 2 cents