I received a Hyperpro rear spring and installed it. It wasn't harder than I thought to do but it took a little longer than I thought it would. It's pretty straight forward to remove the shock assembly. Nothing tricky and no special tools necessary.
Changing the spring is the hard part. Don't believe anyone that says they did it without a spring compressor. I'm not saying you couldn't do it without one I'm saying you shouldn't try to do it without one. And look for a decently built one. The one I used I've used before the the Hyperpro VFR spring was probably the stiffest spring I've done this way. If I do it again I'm going to look for a different compressor.
So it makes a decent and noticeable improvement. I also have Wilbers progressive fork springs which I wrote about earlier. The rear is both stiffer and more plush. Also the harshness has been reduced to very minor. Don't get me wrong it's still a very taunt riding motorcycle but now it's not overly stiff and unyielding. It actually feels like the tires are staying in contact with the road surface. The city I live in has terrible streets, imo. And it's a good opportunity to "test" suspension changes.
For the cost changing the fork springs and rear shock spring are a worthwhile improvement. I'm not saying it's better than custom cartridge forks and shock/spring setup but if you are on the fence you will feel the improvement. If you can't feel the difference then you probably wouldn't feel any difference in a custom setup.
For reference I'm about 197 lbs or 89.5 kg without riding equipment.
The stock spring was about 12.96mm wire, 7.188" long and has about 6 coils. The Hyperpro spring has 13.64mm wire, 7.375" long and about 7.75 coils. Sorry for both metric and inch measurements. :)