I personally would steer clear of this offer if I had a home that will sell on its own. You know what you want to sell for...if they won't pay that, it's no different than saying NO to another type of buyer.
I know someone who recently went this route, and was overpaid by the company, who felt the home was worth more than it was. The house is still on the MLS, and she is happily in her new home. You could always talk to them to get their figure. As a flipper, you probably have a good idea of what your home is worth. One word of warning, if you go this route, DO NOT allow them to market your home during the contract period, but before the closing. This has become somewhat common in this area, where they try to find a buyer at the higher price during the closing process, and if they don't they cancel the contract.
Good luck finding a great buyer!
If you had an agent to negotiate with them I would maybe consider, listening to what they have to say, but as you probably are not as experienced in the whole process, I would probably leave them alone and wait to find a buyer the conventional way.