It was an impulse buy when I saw that Amazon had it for only around $8.50, but I'm also hearing reports that the pen tips that come pre-installed in the on-screen writing implement that comes with the Surface Book and Surface Pro 4 (they both use the same pen) break pretty regularly. So, eventually, if you use the Surface pen for any amount of time, the Pen Tip Kit is actually a pretty good investment.
It's also reasonably priced. You can get the same thing at the Microsoft Store (online and in physical locations) for $10, but as it always does, Amazon provides a cheaper price. And, considering Prime members get free 2-day shipping, I always choose Amazon over any other option.
The actual product was a LOT smaller than I anticipated. I've seen it on display in stores before (Microsoft and Best Buy) but swore it looked bigger there. However, as you can see from the images, the Pen Tip Kit is a little bit of nothing. It's small, but that means its easy to carry and easy to swap tips. It also means its easy to LOSE tips.
Pulling the tips out of the pen feels a lot like playing the Operation Game, and it seems more difficult that it should be. It took me a few tries to get the pre-installed tip removed the first time. At first, I took the Operation Game strategy, trying not to break the tip or have a hidden buzzer go off somewhere. But, I eventually had to just dig in and get a little macho-ferocious and the tip came right out.
I've not had a chance to test each of the tips that come with the kit, but will be doing that this weekend.
Like I said, if you own a Surface Book or a Surface Pro 4, you'll probably need these eventually. It's on Amazon for $8.49 right now: Surface Pen Tip Kit
If you buy a separate, new Surface Pen these pen tips come with it. The new Surface Pen is compatible with Surface 3, Surface Pro 3, Surface Pro 4 and Surface Book.