Composite video has Luma, Chroma and Sync going through the same wire. The sync stripper will remove everything but Sync. This is only needed for devices that need the separate sync signal. The digitizer in the OSSC can extract sync by itself so there is no need for a sync stripper in the cable.
The chroma signal in composite video will interfere with the RGB signals and cause diagonal lines in the video. You need a cable with individually shielded wires to prevent this. I don’t think the cable in that eBay listing has shielding on the individual wires.
The Packapunch cables from Retrogamingcables are known to be properly shielded: https://www.retrogamingcables.co.uk/pc-engine/PC-ENGINE-PCE-DUE-turbografx-16-nec-core-grafx-PACKAPUNCH-PRO-rgb-scart-video-av-cable
If you are using a SCART switch then you also need to use a shielded cable from the switch to the OSSC. https://www.retrogamingcables.co.uk/audio-video-accessories/scart-leads/euroscart-male-to-euroscart-male-rgb-scart-cable-pro