Depends, if you have that many fans ( up to 8 ) that do not connect to the board with their own monitoring systems, and places to put up to 8 thermal sensor, and if your system gets really hot then yes.
Also it looks cool, which is always a bonus.
Price at Plycon is $64.99, they are having a sale at the moment.
I have the DD5 and it's quite an interesting gizzmo. I purchased it mainly for use in my planned water cooling set-up, I hope to be using case ambient temps and water return/delivery temps to control the fans for my case and radiator.
One thing I did find curious is that there are two different types of thermistor, and they measure two different resistances at room temp. The blue ones read 10K ohms and the flat brown ones 11K ohms. There is no requirement as to which socket they plug into and no temperature error compensation - so you get different temp readouts with different thermistors.
When I get the time I intend to check them out and see which id the closest to the actual temp and maybe I can add some resistance in series or parallel to compensate for error. I will post the results when I have them.
Other than that, I quite like the unit and I would suggest that they maybe incorporate a 7v option for some/all of the fans in the next revision, maybe even a two stage temp alarm setting which will apply 7v to the fan(s) at the lower alarm setting, and 12v at the upper setting.