I backed the KS and have the book. The adventure includes a town, small wilderness area, and the manor itself. Experienced players with Tier 1 PC's will be fine. Chapter 3, The Sanctum of Madness, is set in the Wilderness area and is "designed for 4 to 6 Tier 3 characters." There isn't any other specific guidance for PC levels for the Manor itself, but the encounters include typical tier 1 foes. Some areas would require tier 2 PC's. 212 pp. The manor proper begins on p 51 and the appendices begin on p 133.
As to the quality of the product, my review is mixed. If you are willing to put in some study and prep, I think it will be fun for your players. If you want to read some box text and roll dice, this isn't a good adventure. I'm a fan of FGG and also backed Rappan Athuk 5e. I have a nostalgic soft spot for old school modules, and Tegel Manor 5e wouldn't exist if not for the enthusiasm FGG has for old school adventures and Judge's Guild, so I'm in a forgiving mood about the book's production flaws. I haven't read the whole thing but my first impression was, "what the hell is this?" This is one of the earliest published D&D adventures and you have to be in a 1977 mindset which means your players are more interested in finding out what is behind the next door than story-telling. The adventure itself does not have a story arc. The book doesn't lead with a history of Tegel Manor or an overall plot. Your players are adventurers, and this is a place to have adventures, so that's what they're going to do. The manor does not a pose threat to the wider world, there are no rumors of fantastic treasures, and no driving reason why the players want to go there, other than some NPC's in the town might pay them to go there. There isn't any kind of expected progression through the adventure. The players will do some things, rest, and do more things, in no particular order (the last encounter in the manor chapter is just a kitten). There is an abundance of mystery, horror, puzzles and danger to experience and that is the reason to play the adventure.
Overall the book has good text and artwork. It does have some warts that interfere with smoothly running the game, so I think you have to be extra prepared. It doesn't take long to find these warts. On the first page of chapter 1, there is a reference to a burglar stat block in the bestiary, but FGG left out the burglar from the appendix. Not a big deal - just sub in some other NPC - but you need to know that before you go looking for the burglar while running he game. Here is a more serious problem. Many of the rooms refer to someone from the Rump family tree, listed in Appendix I. If there is a system by which these NPC's are organized in the appendix, it eludes me. Each listing reads like this, "2. Reckless Rory (B3.)" They are not alphabetical by name, nor are they are in any kind of order based on encounter area. Occasionally the family members are referenced by number in the text: "the dusty portrait of Radded Rufus (NPC#55)", which is great, but most of the time they are not: "When Lady Rubienna Rumpula is present..." There is no way to find her other than to skim the appendix until you find "79. Lady Rubienna Rumpula (A4.) [F1.]" And once you find her, you are not done. Turns out she's a vampire, so now you have to look up the vampire stat block. It seems like they had a system in mind to refer to the numbered NPC's in the room descriptions, but in the rush to get the book published the system wasn't fully implemented. This shows up in other ways, too. There is a wilderness map in the book. Tegel Village has buildings labeled A to W (get out your magnifying glass because the entire town takes up a 4cm x 4cm area on the book's map). Chapter 2 gives the wilderness encounter areas, labeled AA - HH, but these areas were omitted from the map! Most of them you can figure out from the description, but it's hard to explain leaving a whole chapter's worth of wilderness encounters off the wilderness map! KS backers got 6 panel full-color maps of the manor and wilderness, and hi-res map files which are much better than the manor maps in the book. Hopefully you get those files when you purchase the book pdf.