They are probably the worst letting agency I've worked with. They only worry about getting paid, but if the flat has problems they never return your calls. We've been chasing some missing keys from the flat for a month, and we ended up having to make copies of the main keys ourselves under the promise that they'll repay us.
Not to mention taking 6h to actually give us the keys, changing the terms of the contract at the last second when they knew we didn't have any other option, etc... i am considering talking with the Ombudsman. They are also expensive, with fees of up to 375GBP.