Wow, very pleased to see this got published at long last. As for helping you decide on whether to get it for yourself, the following may help :
That's Gabor Lux's website, he's one of the co-authors, and that site explains and illustrates his design stance when he took on the task of expanding the module.
I can't speak to how much, exactly, survives the 2019 version. What I do remember, from the author's manuscript back in the day, is that it was an utterly idiosyncratic module, off the charts creative, but also often extremely whimsical. Gabor took a house full of a completely eccentric family and he made them... even weirder. Think of Heath Ledger's Joker, or Depp's Jack Sparrow in the third movie's "My Peanut" sequence. Now multiply these characters by the dozen and have them haunt Castle Ravenloft. Boom. That's Tegel Manor.
If the original '77 module was already very weird, Gabor Lux made it both more consistent and even more intriguing. My favorite bit was a random effects table for magical columns. What is pretty pedestrian in most author's hands (or my own, to be honest), became this miniature gem for creating hilarity and tension at the gaming table.
I wish there'd be a cheaper available version, if only so folks would feel more relaxed to try something outside established genre boundaries of D&D modules. I know I'm more inclined to sink fifty bucks into a bucket load of Paizo/WotC modules that, let's face it, re-hash the dozens of modules I already have on my shelves. That's just how we work. "Men hate two things--the desert, and novelty." Borges. So, if nothing else, Tegel Manor is a safe purchase if you wanna get something you, for sure, haven't seen or played before.
[EDIT] If you wanna see a case in point just how idiosyncratic an education Gabor Lux brings to the table, consider the illustration on page 7 (attached below). Gabor is a huge fan of early European silent film movies, and expressed that the ultimate woman in the Wilderlands setting may have found a perfect portrayal in Fritz Lang's 1924 Saga of the Nibelungs. Check the 1 hour time mark here for the inspiration: