Haven't seen / played / even heard of them, but we can get a rough idea of its possible performance just by looking at the picture of the PCB on the web page. Image filterign is teh biggest problem with this single conversion route. Assuming
all the image filtering is done by those three coils in cans that are visible on the photograph:.
An AADE design for a suitable third order bandpass filter, with 8kHz bandwidth and allowing a compromise 1dB ripple suggests image rejection at 125kHz will only be around 30dB. (Top coupled capacitor design, so low side rejectino is better than high
side) Not sure what signals are down there to get through, and a highly resonant antenna will help a lot more with image rejection - but if its for a grabber, you're probably going to use a broadband active antenna.
Can't make out much else from the web page photos, and it give no specification. But such a simple converter concept can't go hopelessly wrong, if you accept the limited image filter that would be achieved with three tuned circuits
If I were to try that approach, I'd got for an IF of 15 - 19kHz, at the top end of normal soundcard coverage, so bringing the image down to 105kHz and making it easier to filter - although there you would just be creeping into LORAN area.
Andy G4JNT
