I use one. My clean out is about 38ft from the clipper and using the slinkies was always a pain as I either had just too short to reach or too much excess. I use the Flo-jet portable version. I hook it up to the RV battery (while plugged into shore power) with jumper cables. I have a 50ft 3/4" hose on a reel and only unreel what I need. The pump works great. For me, it doesn't take any longer because I don't have to "massage" the waste through 40+ft of slinky hose (having to pick it up along the way so the waste continues to drain instead of coming to a standstill mid-slinky).
My waste tanks are each 20gallons. It takes about 10 minutes total to dump.
I wouldn't go back to a slinky for anything.