I'm sure this is good for many things, but it won't make a great digital oscilloscope. A sample rate of 125Msps is not really high enough for a bandwidth of 50MHz in that context. The low-end Rigol oscilloscopes do 1Gsps.
I suspect it might be more useful in, for example, software-designed radio applications which should be able to make use of the full analog bandwidth and the much better dynamic range.
They time interleave four Analog Devices AD9288 [0] dual 100MS/s 8 bit ADCs that are over clocked to sample at 125MS/s (so 125MS/s times 8 = 1GS/s).
What's fascinating is a number of people in the HW community have managed to reverse engineer the Rigol DS1052 scope. A Hellene on the EEVBlog forums has lovely pencil drawn schematics [1].