Hello Vegas,
It does sound like there’s no reason for you to consider one. If the fretboard size is most important and the 17” scale is what fits you, then stay right there.
These kinds of Ukuleles are near and dear to us – we build a number of complete and “integral” long scale instruments – among them what we call a Tenor Largo. By integral, we mean designed from the ground up for the longer scale.
Our scale is 20” and the body is designed to be proportional to the neck, as opposed to the standard way of doing things – just sticking a longer neck on a standard body. The standard bodies tend to be short and wide. As far as sound goes, it will work pretty much the same either way, but we think a longer, narrower body just looks better with the longer neck.
If you play up the neck a lot, then one big advantage comes there. Properly strung, you'll get clearer notes when you play up high. Even if a 17" scale is more comfortable for you in 1st position chords, chords up the neck can get cramped - 20" feels pretty good to most folks who "play up" a lot. And you get the fretboard of a cutaway (ours has 16 frets to the body - 20 total) on a traditional body shape.
There aren’t any sorts of generalizations you can make about sound until you factor in the tuning / strings. Apart from the comfort factor, these are the real reasons for a longer scale. In the case of a Tenor, and without going into all the particulars, if you like tuning to a reentrant C, the huge majority of players will prefer what they’ll get from a set-up on the 17” scale.
Tune down, and things start to change. Your options for stringing start to give better tensions, more clarity and better projection. At reentrant B flat either scale can be nice. Down to A tuning and the advantage starts to go to the long scale. Tune down to G and there’s no contest – long scale, all day, every day. If you consider that most Tenor bodies can handle a g note and that the Tenor was originally “designed” for that tuning, then the real question becomes “why weren’t they built with a longer scale from the start?”
As far as Linear tuning, it depends on your preference in sound. If you’re tuning to C, your low note is again a g, so generally no problem there. If you like wound strings give a slight edge to the 17” scale though on 19-20” a wound set-up is still good. If you like plain strings, however, then once again, long scale, all day, every day. The flubby, loose or dead plain 4th string g note you get with the 17” scale improves dramatically at 20”.
There are those that think of putting a linear G tuning on these instruments - like a traditional Baritone. That's where you get into the sort of thing Ian was likely referring to. The body is still a Tenor, so your notes won't ring clear below a g.
By the way, we’ve always felt that for plain string g notes, 20” does a better job than 19”. The reason you find 19" most of the time, is that there are cases out there that will fit them - the extra inch puts you in a custom case.
That’s our take.