Voltas is a TATA product and is one of a few brands that have sustained themselves in the market for a long time.
The features of their all weather ACs include:
a) a compressor that provides instant cooling at even 52 deg. While this is good for bringing down your room temperature quickly, there are limitations to how much difference in temperature( between outdoors and room) that a compressor can induce. Hence, at those high temperatures, there will certainly be a loss of cooling efficiency.
b) dehumidification takes place automatically in any AC; normally the humidity inside the room is brought down to somewhere around 50% rh, which is quite comfortable for the normal human. Any further dehumidification process involves heating the air to some extent, which would then involve more power being consumed.
c) There is a heating element in-built for winter, which is redundant for Chennai weather; this would probably entail paying for a feature you would never use.
Reg pricing, these are market driven and would be very similar wherever you buy it from. To select a store, it is suggested you visit their website and choose from your locality. The only caution is to ensure you get proper installation and prompt service.
I hope this information helps you make an intelligent and educated purchase.