I think Grumpymouth's point is very fair. It would drive me up the wall if I'd moved into a "residential" development and then found the place being rented out by the night. It's almost certainly breaking the terms of the lease (unless it is the devloper themselves renting certain apartments out en masse rather than a private investor chancing his arm) and I can imagine the many social problems that come with short term lets must be intensely frustrating for long-term residents.
But lets be fair MDHtravel is staying as a family so I'm sure they will be entirely responsible guests and it has to be said that half of Manchester city centre currently seems given out to short term let apartments of one sort of another. If they can get a good deal at a good apartment that suits them then thats their prerogative.
One of my employees lives in Abito and they love it, in fact they are just in the process of renewing their lease. The reason the flats are cheap (to buy, rent or stay) is that they are small, the location is in a non prime end of town, and they use the pod system of fold away beds and multipurpose living areas which are not to everyone's taste.
The area is still pretty run down (surrounded by building sites, carparks, train-lines, lock ups and light industry) but in all seriousness do not let this put you off. You are a minute or two's walk from Deansgate and the heart of Manchester (well the cathedral, Urbis, the metrolink, Selfridges, Harvey Nichols etc...) and I've never found an ounce of trouble walking around that area day or night.
As to whether that apartment in particular is one to go for I don't know. Is the mention of sales/city taxes a generic thing on the site or for the letting agent or does this specific advert mention it for this specific apartment? I can't believe it would be a scam to be honest - more likely to be lazy proof-reading - but hey this is the internet so if you feel the slightest doubt then look elsewhere.
One thing I will say is that the photo of the flats is misleading. Only the main building has been built and the surrounding redevelopment is unlikely to happen now with the credit crunch slaying property companies left, right and centre.