This debate is entirely about whether the Tories are up to the job.
I think it's more about whether the conservative MPs want to keep their well-paid jobs. I doubt that many (if any) will vote to say that their own party is incompetent. With the active support of the DUP the vote seems a foregone conclusion.
Any Conservative MP who voted against their own party would likely be de-selected by their constituents for the next election (whenever)

There is a fair amount of truth in that, Nigel, but of course it applies to every confidence vote (on the government), for any party, at any time. There is nothing special about this one, in that respect: self interest is always a significant aspect. Occasionally, an MP 'sniffs the wind' and thinks the movements under way mean that there could be a change of leader/direction coming, and their long prospects at better supporting the new rather than the old, but that is pretty rare.

I (and if I read him rightly Steve) think Corbyn did not want to call the confidence vote at this time, because he then has the difficult problem of what he does next. I have heard some comments saying that just because Labour does not get a general election this time, it does not mean they won't on another occasion, so they will stick with the 'try for a general election' strategy. I think that would play very badly with party memebers.