I have had a discussion about this in email, on the subject of replacing RS232 interfaces with either of these two options.
My points are that if the item only needs local connectivity (ie download data, setup machine etc) then a generic USB solution such as provided by the FTDI modules is adequate, rather than have to go through having to redesign an existing product. Field service seems to be one application where the technology has run forward (you try and find a laptop with RS232 on it these days). Yes you could use a dingle, but then doesn't Windows keep changing the port number for you?
TCP/IP is nice, but if you don't need the machine permanently connected to a network or just have a basic interface, it may be too good a solution. Yes, you can add extra features and a web interface, but would a water level monitor (for instance) that only communicates twice a year need this?
