> I use my keyboard everyday but I wouldn't pay $20 per month for it. In fact, I paid around $4 total for it, as paying more would bring significantly more diminishing returns.
I wouldn't pay $20 per month for a keyboard either, but I doubt that a $4 keyboard is even close to diminishing returns unless you got a really good deal. Even $100 for a decent mechanical keyboard is not much if you use it for many years.
If you really think you won't get anything out of it then no it does not make sense. I can only speak for myself, but I prefer the feel of my current keyboard over any I had previously. If you happen to be fine with the rubber dome response then sure, but mechanical has a much wider range of options. I also find it easier to clean (by taking off the keycaps) and more resistant to liquid splashes (collects under the keycaps and doesn't tend to get into the actual switches unlike my previous rubber dome keyboard where any water getting into the caps meant having to take it apart and drying the rubber layers before you could use it). But those points aren't something a cheaper keyboard couldn't inherently manage as well.
I wouldn't pay $20 per month for a keyboard either, but I doubt that a $4 keyboard is even close to diminishing returns unless you got a really good deal. Even $100 for a decent mechanical keyboard is not much if you use it for many years.