My partner and myself found a flat through Dennis and Hayes and lived in the flat, which was managed by them, for a year. My overall experience with them was very negative. When showing us flats they were borderline rude, seemed to know little about the properties we viewed, and on more than one occasion brought the wrong key. However they had a place that we liked so we took it.
However, having the property managed by them was the real headache. It would take weeks, sometimes months of pestering them to get a workman sent out for maintenance, including a leaking pipe that was causing water damage. Toward the end of our contract we thought we could smell gas in the kitchen and asked for them to send someone out but they laughed it off and said we were imagining it. As it turned out there was a small gas leak and it actually made us ill as a result. They only did something about this once we got to the end of the contract and new prospective clients complained about the gas smell.
In short: stay away, especially if it\'s a property managed by them. It may end up effecting your health!