Yes, can be off in their dimensions.

Some have had success with them, others haven't.

A common brand, Keyster, stamps their calibrated parts with the same numbers as what was in the carb.  But Keyster will tell you that their calibration is proprietary and not the same as original.

In the Honda world the kits seem to work...  I have had so many issues with Yamaha Enduro carbs that have had "kit" or aftermarket jets installed that I always look for the genuine Mikuni "square within the corner of a square" stamp that they put on every jet, slide, and slide needle.

Amen to that.  30 mile old  genuine piston and cheap aftermarket jet combo.

Ouch! That hurts.

Are those CMS carb parts Mikuni parts. If not where can you find original Mikuni parts? 

"Are those CMS carb parts Mikuni parts. If not where can you find original Mikuni parts?" 

As long as the item doesn't say "Alternative...", then yes.

If still available from Yamaha, obtain through your local dealer, fleabay, online etc, using the Yamaha part number. If not, then contact a supplier of Mikuni carb parts - here in the UK we have Motocarb and Allens, and an online search should identify similar companies in your part of the world.