I stayed 1 night to cut my car travel into some shorter legs and was looking for an ETAP as you usually know what to expect for a very reasonable price.
Having stayed in several ETAP hotels before, this one in Mainz south was a positive surprise as it seemed to be either newer than others or recently renovated. You get what you pay for: a bed, a shower, a clean room. What i find worth to remark is the free WiFi access which is still not standard in some far more sophisticated places. The easy access from the motorway was an additional criteria which made it a good choice for the purpose of my stay. An additional asset that comes with this ETAP is the supermarket in the back of the building: normally ETAPs are in the middle of nowhere but here you can do some shopping a few steps away.
I personally do not like the sleeping comfort that much, but for 1 night to relax from driving it is absolutely OK. The shower is tight, but sufficient and (taking the risk to repeat myself) it is absolutely clean in the rooms.
I had no breakfast and no contact with reception, so unable to comment on this.
Overall the ETAP hotel provides a good value for money, a calculable experience in a slightly sterile environment.

If you are claustrophobic, then this place will not be suitable as the toilet is small, windowless and makes you feel locked in.

Although the room is small, it's clean and tidy. It reminds us of the days in a student's dormitory but with the added luxury of private facilities. The shower has a most interesting door with a hole (see photo)! So one has to be extra careful to avoid splashiing water all over the carpet. Also bear in mind this means you will not have any privacy both in and outside of the shower!

Breakfast is basic but adequate. Free in-room wi-fi is available. Tea/coffee/snack vending machine is available in lounge. There is a supermarket next to the hotel, and a nice, cheap trattoria / pizzeria nearby. Overall, it offers good value budget accommodation with easy access to the city centre.

Pillows are to soft. Should consider having thicker pillows or two pillows for each bed.
Shower area a little too cramp and no place to hand clothings inside shower. Not so suitable for two persons to stay in a room unless they are a couple.