To summarize this, I’d say:
- there is very little chance that the phone won’t ship. I mean, you never know if NXP is hit by a meteor tomorrow, but…
- maybe they butcher the April promise and it will be May or June
- maybe the phone doesn’t work (well) with the frequencies your current carrier uses
- maybe, the initial release will be too unstable for you to rely on it in every day situations
- quite likely, the initial release will have quite a few features missing that you’d like (e.g. GPS navigation)
Anyway, that will not make it a paperweight. You could try a different carrier (or modem!), give it a few more weeks, install the updates and the nice apps others will add (and are already working on) and you will feel very good having been a supporter from the first hour.
As it has been pointed out, the battery drain bug (described here) is on NXPs side. That Purism figured that problem out very early after they got the chips, and work with NXP on fixing it (instead of just concentrating to get the dev-kit going, that doesn’t need power-save states) and being very transparent about it, should, if anything, reinforce your trust in them.
As Todd Weaver has been saying many times, it was always the plan to do a phone, but first build some laptops, because else nobody would have even considered they could do what many failed to accomplish.
However, what you have to keep in mind here: Most of the “failed” ones did not fail because of technical difficulties, but rather because they didn’t see a sufficient market for the product. This is very different with Purism, because (big*) profit is not the main goal.
They also don’t try to create their own eco-system, but rather enhance the existing GNU/Linux/FOSS/Gnome/KDE/UBports ecosystem for the benefit of everybody. And because of that, existing Linux developers will not be reluctant to develop or adapt apps for the Librem 5, because it so close to what they always do and would not be wasted if the phone would not succeed. Every app for the Librem 5 should reasonably well run on any Linux mobile or desktop device.
(*) Sidenote: They originally promised to deliver the phone if ~2500 pre-orders would be placed. That’s not much, especially if you also want to make big money 
Meanwhile, extrapolating my old numbers, they most certainly have at least 4500 devices preordered, but I’m pretty certain it’s already more than 5000. And every order on top will make the phone better.
As @dcz said, have some faith. There’s no indication that you can not trust in what Purism is saying. Except for the inevitable delays, Purism has a very good track record of delivering what they say they will.