telc publishes a free official model test (Übungstest) for Deutsch B1 with audio and answer keys, and sitting one under real timing before you book the exam is the cheapest way to find out whether you are ready.
telc publishes free practice material for Deutsch B1 on telc.net: the question papers, the Hörverstehen audio and the answer keys. This is the material to start with, because it is written by the people who write the exam.
Exam centres frequently hold additional practice papers, and public libraries in Germany usually stock telc preparation books. Commercial preparation books are useful for drilling but are not the official format - check the structure against the official Übungstest before trusting a book's layout.
A model test done casually tells you almost nothing. Done properly it is the single most informative thing you can do before booking.
Time it strictly, including transferring answers to the answer sheet. Running out of transfer time is a real way to lose real points, and it only shows up if you practise it.
Do the whole written paper in one sitting. The 150 minutes is partly a concentration test, and splitting it across two evenings hides that.
Do not look up words. No dictionaries are allowed in the exam, and looking one up during practice converts an honest signal into a false one.
Say the oral parts out loud. Reading them silently trains nothing. If you have no partner, speak your side aloud anyway and time it.
It marks itself for 180 of the 300 points. The other 120 - Schriftlicher Ausdruck and Mündlicher Ausdruck - are assessed by examiners against four criteria each, and you cannot apply criteria to your own work that you have never been trained on.
This matters because those are the two parts that must be passed independently, and they are where most failures happen. A candidate who scores well on the self-markable sections can still be unprepared in exactly the place the model test is blind.
This is what the simulator is for. It runs the same structure under the same timing, and then scores writing and speaking against the same four criteria the examiners use - reporting which criterion cost the points rather than a single number. The free official Übungstest and a scored simulation answer different questions, and it is worth doing both.
Yes. telc publishes official practice material (Übungstest) for Deutsch B1 free on telc.net, including the question papers, the audio for Hörverstehen and the answer keys. Exam centres and libraries often have additional past material.
Two or three full ones under real timing, spaced out - one early to find your weak section, one or two in the final fortnight. Doing many more adds little, because the format stops being new after the second.
For reading, listening and Sprachbausteine, yes - those are marked against a key. For writing and speaking it cannot, because you cannot assess your own work against criteria you have not been trained on. That is the half of the exam where most failures happen.
Yes, including the answer transfer. Untimed practice trains a different task from the exam. The Leseverstehen/Sprachbausteine block especially - its whole difficulty is that you allocate the 90 minutes yourself.
Sit a full simulation under exam timing and see exactly where your points go.