Well, if you have to use shell that's one thing, but I would be hesitant to use such a large shell script for something as important as certificate issuance in an environment where I didn't have to.
Just as a counter point, I've been using acme.sh for ~3 years now and it's been rock solid.
I get your point, and was pretty shocked to find acme.sh, but after the certbot PPA made a giant mess of my system I gave it a try. On the other hand, why should I balk at running thousands of lines of bash, but be fine with thousands (or many more) lines of C, Python, PERL...? You can write crappy or beautiful code in any language...
