I agree the CW decoders are practically useless in contests...too much close-packed QRM, often within a few Hz...and the contest exchange is so short that any bonehead can copy what is required for the contest log (a callsign and zone, for example -- the "59" or "599" is filled in by the contest logging software!).
I own, and have used, the MFJ keyboard keyer. It works great (not contesting, just general purpose operation, ragchewing, etc), is RFI-free and has zero problems. But it's just not fun! I think a lot of the fun of CW operating is sitting back and listening to what the other station is sending, and then sitting up to send with a paddle...the fun is diminished by too much automation. At first, I liked the MFJ because it allowed me to reply immediately to comments or questions posed by the other station...such as, if the other guy said, "WX here is very cold, we had two feet of snow today..." I could immediately send into the MFJ buffer memory, "Oh, too bad abt ur WX, here it's sunny and warm..." and do this while I was still listening to the rest of his transmission. I'm a fast typist (about 120wpm), so keying in quick comments like this only takes a few seconds and doesn't distract me from the QSO.
Then, all my comments are stored in the MFJ buffer, and when the other station turns it over to me, I just hit "enter," and if the speed is adjusted to 20wpm, the machine will send several sentences without me doing anything. I could literally walk out of the room for a cup of coffee, and come back, and "I" would still be sending! That seemed like fun, for a while.
But, after a while, like most anything new, it just wasn't fun. Not nearly as much fun as using the paddle, making occasional mistakes to prove my humanity, etc. Automation for contesting is fine and helps improve scores. Automation in everyday life is, um, boring-?
73 de Steve WB2WIK/6