So far, I've tested against:
(1) Pareto Data Recovery
(2) Softonic File Scavenger
PDR couldn't find the "securely deleted" text file 'unrecoverable22.txt' at all.
SFS found it, but it found the version my code had overwritten the original as, namely a zero-length file with file attributes showing creation/modified dates in year 2036, as shown below (in other words, what it found in no way resembles the original file). Rather it found the truncated, false-attributes file my code creates before calling File.Delete():
Safe programs for File Recovery
So, thus far, I'm pleased with how my code is holding up...