eSynic HDMI to SCART Converter, 1080P £4.99 with voucher @ eSynic UK / Amazon

It seems to be the wrong way around to be useful for most people.

A SCART input to HDMI output would allow people to hook up older devices (e.g. Wii) to a newer TV.

This is even more niche.

If you want Scart to HDMI then devices/cables start around £8

Decent price for what it is, but I think its important to keep expectations for quality in check with something like this. Might not necessarily matter for everyone, mind you.

At this pricepoint the HDMI won't be converted to the full fat RGB SCART (the good stuff).

Rather, its converting things down to Composite (yellow video, red and white sound) in a SCART form factor like many cheaper boxes. Composite being the 2nd worst analogue signal you might get your hands on VS RGB which is arguably the best (Component is also brilliant and has its place). And the downscaling on this box may be questionable and laggy for most niche gaming uses (and passable for other uses).

Might be useful in a pinch and a last resort, but it really won't take full advantage of the capability of any CRT TVs or older gen flatscreen HD TVs with SCART support.

Downscaling HD content and achieving full-on RGB with target resolutions of 240p, 480i, and 576i at low latency is quite niche and can get rather pricey and/or DIY intensive from my experience. It tends to be in the realm of niche/boutique devices like the GBS-C, Retrotink 5x, OSSC, Framemeister, and various Extron scalers.