12-Fret Slotheads, Yes or No?

Not my favorite, but a lot of people like them. Martin does a better job with smaller bodies than other brands, too. Other brands do deeper bodies and things like mahogany tops which make them even more boxy. I think because I tend to play an acoustic more like an electric, guitars that sound a bit more squishy don't work as well for me, and that's true of 12-fret guitars in general. What is squishy to my ears is warm and charming for others, and really well suited for milder singer/songwriter stuff. If I bought a 12-fret steel string that would probably be the one as it is probably better balanced.

Stringing tips:
-pre-clip your strings. You still need to get a bit of string on the other side of the hole because it will slip a bit, and it isn't a big deal to go in and clip an excess of 1/4" or so if you leave too much, but getting most of it off up front helps.
-First wrap on the opposite side of the post of where you want the rest of the wraps. Doesn't do TOO much, but a nice lock.
-String order should go from the ones closest to the nut outwards. For example: Low E, A, D, then high E, B and G. Same for any slotted peghead.
-Don't hook the string, if that's a thing you do. I normally do, but skip it on steel string slotted pegheads. Not worth the hassle.
-When removing strings, clip them somewhere in the middle. This loosens them up a lot and lets you unwrap it a bit, which you can't really do as well with a whole string, and definitely can't do if the ball ends are still in the bridge.
-Power winders are appreciated more with these.

I love slot heads. I've had several over the years, never had aa bad one. Sold several I should have kept.Recently bought a Collings 001-T, best guitar I have ever played. Fantastic sound for such a small guitar.

I have an Eastman OM that I got not too long ago. It's a fine guitar, sounds great.

But it's not quite what I was after. That would be a smaller guitar, probably an 00 of some kind. Twelve frets and a slothead would be great.

The slot head probably impacts tone, but it is hard to say how because it is rarely a design choice made in isolation, and only along with other things... like making it a 12-fret.

12-fret is less about the length of the neck (though that isn't unimportant) and more that the body shape changes. You have more air cavity in the guitar because it is going up further. Ervin Somogyi has pointed out that on a 14-fret the bridge is half way between the transverse brace and the tail block, while it is off center on a 12-fret; as the neck is buried further into the body, so the bridge has to move back. On a classical (which are almost always 12-fret) the bridge bisects the space between the tailblock and the lower transverse.

To the people who love it, they are warmer, deeper, rounder. To people who don't like it, it is indistinct and tubby.

After playing the Collings for 2 days, I decided to sell 6 other guitars. Knew I didn't have time for them anymore, just kept my Martin 0018 and the Collings plus one little Cordoba C9 Nylon that seems to follow me around the house

My Yamamoto Talus VS-12 (paulownia top/cocobolo b&s) would very quickly dispel the notion of indistinct and tubby sounding. 

Oh, man, what I wouldn't give to spend a couple hours with that old Martin!

That Martin at Ederlys would be a nice way to spend an afternoon.

No its a Larrivee 00-50

I wanted a 000-15S back when they were available new, but never did it - in large part due to restringing fears. I do love the sound of a hog 12 fret.