It seems to me that a solo sailor needs three self-steering arrangements.
The first is a wind-vane of some sort, for open-space sailing; ergo, anywhere where there's at least 10NM between you and land, and no other bugger around.
The second is an electronic helm
, to be used for close-quarters sailing or as a temp back-up for a failed wind-vane....temp meaning, while you fix the wind-vane.
Third. When all has gone to hell in a hand-basket, bungi steering
I must admit I kinda quite enjoy playing with this method. Sure, about the best one can hope for, unless the wind is both steady and true (which happens once every 802 years) one can expect a best result of about 30 degrees either side of a chosen course. But hey! So long as you're pootling around in a few thousand square miles of clear ocean, what's a 60 degree yaw between friends.
I've found that my old girl will play along very happily on a tight reach with bunji. I use up to four wraps of 6mm bunji from tiller-end to solid taff rail. With a jamb cleat to allow me adjustment.
In lighter winds I might use three turns from taff to tiller then cleat. In high winds, especially gusty and moving 10/20 degrees, I might use six turns.
Sure, there's a lot of pissing around with sail-trim, but once there, I can often get an hour out of the system keeping me on a generally true heading.
But when it all gets just too much, and I need some rest or sleep, and I'm miles from everywhere, I simply hank a number four headsail onto the inner forestay, stow all other sails
, sheet in the little'un, go about, leaving the little'un sheeted to weather
, lash the helm
to leeward and chill out for as many hours as I feel the need.
The leeward lashed helm wants to make my old girl go about, so up she comes into the wind. The windward sheeted headsail say, 'No way'! and pushes her nose to leeward again. Helm and headsail tussle it out, but neither ever wins, and I can relax for as long as I want, while I imagine dark thoughts about the maker of the self-steering dingus which has failed.
This practice, well known by ancient mariners such as myself, is known as 'Laying-ahull'.
One can use this tactic even in confined areas when all self steering
has failed, the crew has got a dose of the conniptions (and thus useless) and when one needs a few minutes to get something done.
Even in a 30/40Knt breeze, when laying ahull, you boat will make less than 2 knots.
If you need to do this with the main still up, that's okay. Just let the main fly free then sort it out when you're ready to come back on the wind.
And when you've done what you need to do, you simply flip off the windward headsail sheet, sheet in again to leeward, and go about your business.
I've laid ahull in some quite furious conditions. The more furious the smaller the headsail, but the result is the same. And remember, when laying ahull, you're nearly always pointing in a similar direction to a broad reach, so you're quartering the seas.