I will just order this SDS1202X-E and run it through it's paces. I totally agree to have the scope give you the best information you have to "feed" it at least one or more waveforms to get the picture.... I was able to measure in the 5.xx Hz range, sub 10 Hz with my Hanktek DSO2C15 and thought a "better" scope - Siglent - would have equal to or better performance than a scope half the cost....
I'd highly recommend you consider the SDS1104X-E instead. I know it is more money, but it is also much more than a 4-channel version of th SDS1202X-E. I wouldn't generally rate scopes based on one seldom-used (by most) feature, although of course you should consider what is important to you.
The 1104X-E has 3 different frequency counters. The first trigger-based simple counter, the most basic, goes down to 10Hz. The hardware counter is reciprocal and goes down to 2.00000Hz, although it appears there can be issues with this at the very limits depending on your capture length and so forth. The measurements menu has a frequency counter that works explicitly with the screen capture so you have to set the scope up correctly to get this to work. However, it goes well below 2 Hz, although with not so many decimals. I'm conducting an experiment now to see how low I can get it to go--I'll post it in a while.
Finally, you always can use the cursors and measure frequency manually. Since the slowest sweep speed is 100s/div, in theory you could get down below .001Hz. You would have to be very patient!