Using a Sprocket for COG Gear

First I think your training premise is flawed in that extreme gearing will make normal gearing feel easier. If that's the case either grind your big chainring up some long climbs and see how that helps you spin or maybe whip your legs like crazy down some long downhills for a while. If you want to work leg speed, then ride easier than normal gears, just going down a cog or two from whatever feels most normal is usually enough or stay in your small chainring on faster sections until you develop the suppleness and muscle coordination to spin more comfortably.

But I doubt that cog would work for you anyway, beyond the obvious challenges of mounting it to your bicycle you'd almost certainly have chain wrap problems on a cog that small. Also it's not clear that it's even a half inch pitch cog or clear how thick the cog is but it doesn't look compatible with most modern chains.

There are plenty of low gears on stock road bikes to work on spinning fast cadences in most situations and grinding huge gears slowly will not help you develop the muscle coordination and timing required to spin smoothly at high cadences.

Spacely Sprockets or Cogswell Cogs?