Q&A with NxProse

Showa Sauna not being opened is probably the biggest. I reported that fake bosses were still spawning, and 90% of them were removed in the real patch (and the patch after that 9% more were removed, there's only one or two still spawning right now.) Also the bot-catching monster in El Nath was taken out because it couldn't be killed. There's a few more really big bugs that I can't think of at the moment (I had a list of at least 6 major bugs which were fixed, I can't find it now). I also reported a dozen or more spelling and grammar mistakes, at least 10 of which were fixed in the last patch.

At the very least, the test server gives them one more weak to work on fixing big problems, so if it would have taken 2 weeks to fix, the bug will only plague the real version for half as long.

weeks Isaac, not weak xD

Ive been in all 3 Tespia rounds so I'll say this:

Tespia 1: Pets were glitched, reported and... still glitched.
Tespia 2: Pets were still unfixed along with a few other glitches (oh gosh, I really dont remember them but I do remember the version of Tespia we got being transported directly to GMS)
and Tespia 3 is already listed above.

Ive personally found Tespia pretty "misused" as though we reported bugs, they werent fixed and Official just got the exact same thing that we had in Tespia.

That being said, if they actually did take the info given to them from tespia users and implemented the necessary changes, then it would be well worth it.