Don't worry, completely bricking a TI-68k calculator or TI-Z80 calculator is hard
The newest ttstart versions are not known to crash TI-68k calculators.
Even though I'm maintaining ttstart, I've been using the SuperStart FlashApp, by Greg Dietsche (with some code and tests of mine), for many years on my calculator. I'm advocating to use sstart instead of ttstart, as it has features that ttstart cannot have (or at least, not easily):
* sstart has a lower RAM consumption because, as a FlashApp, it executes from Flash, unlike ttstart;
* sstart is much bigger than ttstart, but it usually occupies an area of memory, in the sector(s) reserved to FlashApps, that would be otherwise unused; ttstart takes up a bit of space (~1 KB) in archive memory. If the FlashApp sectors aren't empty enough for a ~5.4 KB application to be written there, however, sstart will appear to consume 64 KB of Flash memory, but that doesn't occur very often.
* the integration with the home screen line is nice to have; it's harder to do it with ASM programs, because there needs to be a TSR part, and TSRs (like program launching) are a mild pain, due to the silly RAM execution protection that TI put into the ASIC. On the 89T, using HW3Patch or equivalent (say, an OS modified on the computer side by tiosmod+amspatch) is mandatory for TSRs.
Bottom line: you should use SuperStart