Ours came with the boat. As they are no longer made I assume you must be considering buying a boat with the system fitted?
As to recommend, I have no comparative experience, but it works well and puts out the heat, although we have not used it much. It started first time after not having been used for 4 years as the boat had been laid up when we bought her.
It is a bit noisy - but I guess they all are to some degree - not so much if you reduce to half speed. The clicking of the pump is a tad irritating.
One thing I discovered, when the system is switched off, there is a fair current draw unless you then move the Full/half speed rocker switch to the position which extinguishes the red neon.
With the neon glowing there is a 0.3 Amp drain which is bad news if you leave the boat like that /forums/images/graemlins/frown.gif
Not something that you might expect as a neon alone draws a few milliamps.
Another limitation that is mentioned in the installation instructions, but not I think in the manual - on the boat so can't check - is that the lowest fuel level in the tank must be no more than 1 metre below the pump in the heater.
Whoever originally installed ours either did not read this or measured wrong, as there is an additional fuel take off pipe in the main diesel tank, blanked off. The heater is supplied by a separate outboard tank in the locker. This takes up an inordinate amount of space, so I am looking to supply from the main tank with an electric pump. Job for next winter.