Regarding these scopes (in general):
Unless you absolutely, positively need a scope, and you have no other means to diagnose a particular issue, take the money you would've spent on one of these, and put it away to save it for a real scope.
These small "pocket scopes", while neat in and of themselves, aren't much use beyond mostly "audio frequencies"; the bandwidth of these is supposed to be "1 MHz" - so in theory you need 5x the bandwidth of your highest range signal, so you could only measure with one of these up to about 200 KHz.
For about $4-500.00 USD you could get a 100 MHz 2-channel DSO brand-new. If you look carefully, you could get a used scope (may or may not be digital or DSO, though) for around $200.00 (but beware - only purchase if you know how to test out such a scope and you can test the scope out yourself, in person - or if you buy it from a re-certification seller that guarantees the performance).
In the last 9 months, I have purchased two different used scopes, one analog (Tektronix 2213 - 2 channel, 60 MHz), one a combination analog/digital DSO scope (Fluke Combiscope, 2 channel - 100 MHz) - both name-brand, both calibrated, and I have spent less than $400.00 total on both (maybe I should've taken my own advice, but then again you're not going to find a Fluke or Textronix DSO scope new for $400.00).
These pocket scopes are "fun toys", and probably have some use for the "field bench" (although there are much better "pocket" DSOs out there if you are willing to spend the money), but if you think you'll need something more serious and can wait - save your money.
