Hotel Blumenstein is a clean, comfortable, and reasonably priced (by Swiss standards) place if you need to stay in Frauenfeld. Be aware that the hotel runs on a very low-staff model: guests check themselves in, there is no desk staff, and contact is by phone.
When I checked in, the self-checkin machine knew my reservation, but was broken and couldn't accept payments; when I called the attached help number, there was an immediate answer and I could give my credit card number by phone, so it worked out OK. The breakfast is modest but acceptable, and the daily cleaning staff is very friendly and supportive. When I requested an extra pillow from the cleaning person, there were two there the next morning.
My one concern was security. With no desk staff, there is no way to use the hotel's safe, and the individual rooms do not have safes. Moreover, the two hallways of guest rooms are off a public stairway that is open during the day, and that serves several businesses. That means anyone could walk in off the street and be at the room doors in a moment, since the hall door with a keycard lock was not usually closed, at least not during the day. Not a major concern for me in a small, safe town, but still not ideal in terms of controlling access to the guest area.
I was comfortable, the room was clean and everything worked, and the location is extremely central, right opposite the train station.