They work - although combined washer-driers always suffer from the problem that they can never dry as large a load as they can wash. Provided that you let them run through to the end of their cycle (including the ten minutes of cold air circulation at the end), they leave the clothes as dry as an open-circuit dryer.
Reliability can be an issue in cheap models: you've got a drain pump running, and a solenoid stop valve (for the cooling water inlet) energised, continuously. This is a significantly more arduous duty cycle than in a washing machine, yet the same components are often used. Once you lose cooling water, you can get consequential damage to the blower.
A.