On the specs page for the DSO nano I see that the ADC they are using is 1 MSPS. The cheap Rigol, for example, is 1000 MSPS. All I can say is that the DSO doesn't look all that appropriate for high-speed circuits (it tops out at 1Mhz and does that on 1 MSPS which is cheating). It seems more suited towards audio gear.http://www.seeedstudio.com/wiki/DSO_Nano_v2#Specifications
I fully agree that the DS0 Nano is not good for high-speed circuits. However -as we are on the Arduino forum- I assume high speed circuits is not the target of fkeel.
I bought the RIGOL deal which was the 50Mhz scope and their Arbitrary function generator. I use the scope all the time. The only time I used the Arb was the first time I turned on the scope...
The big question about the function generator is "What do you plan to do with it?".That'll tell you how much speed and precision you need, whether it needs to be especially portable, etc.You could well find that something extremely cheap and simple (like a 555 astable for square and semi-sawtooth waves, and a couple of other simple circuits for other waveforms) will more than suffice.If you don't need "portable", look into old HP and Tektronix rackmount units, that are probably available for peanuts now.
about Function Generator an other good idea should be using AD9834- it is a SPI interface chip - it is produced by Analog Devices - it is able to generate signals up to ~30Mhzi mean, you could build up an home-made board =P