LF Spectrum analyzer

[Telstar]

I'm considering a spectrum analyzer, but I need it capable to perform at LF (at least 50hz) with low noise and very low THD (about -130db), up to 1Mhz or even few khz.

Doing some googling, I came up to this:
http://www.aaronia.com/products/spectrum-analyzers/NF-5030-X-Low-Frequency-USB-Analyzer/#details

Has anybody used their instruments? The customer portfolio is impressive, mostly for EMC analysis, but this model seems to meet my needs.
I'd like to know the noise and distortion specs, though.

Other suggestions? New or used, usb or not, the budget is 1k, more or less.

[free_electron]

DSA . they are (were) made for this kind of stuff.
You can find used ones on fleabay for around 600$.