I, too, purchased an IN1508, and, while I think it’s a really neat device and does what it’s supposed to do well, it doesn’t do what I want/need it to do.
I was very displeased to find that its scaler cannot be disabled–which kind of makes sense, since it’s a presentation scaler, not strictly a scan converter; so it forces you to select a specific output resolution and then scales to that–and it will apply deinterlacing to 240p content over S-Video and Composite whether or not you want it to.
After the IN1508, I tracked down a Kramer FC-4044, which works great fine–it will take an S-Video or Composite source and convert it to YPbPr and RGBS without any additional processing. Sadly, it introduces a ton of video noise; I have no idea why it does that or how to fix that, and, weirdly, running it into the IN1508 eliminates the noise. ¯\_(ツ)_/¯