You can't really go wrong when you have clear goals and recognize where your skill set has a gap.
An aftermarket speedometer is, like most mods, little more than a glorified bolt-in item, easily swapped-in and changed back...when & as you like. Mothball your original speedo and you'll always have the option to resintall/restore it later. At the very least, unmolested, it's an appreciating asset.
If you happen to like that particular KOSO unit, go for it. The bottom line will be close to the cost of restoring a K1 speedo with bad chrome, taking dollars out of the equation. There are a lot electronic gauges on the market and the number is growing, while prices are becoming more reasonable. If you're looking for something at the lower cost end you might take a look through the Trail Tech catalog. KOSO makes a number of other gauges, ranging widely in price points. At the higher end of the spectrum, Acewell, Dakota Digital, Motogadget, Stewart-Warner and Autometer all offer electronic speedometers. It boils down to personal taste and budget.