I've added the Kiwi upgrade to mine, and I would say: Go for it!
To me, the interface is much easier to use than the original, as long as you have the graphic of the menu path handy. Yes, that sounds confusing, there's more "stuff" to keep up with, but the editing makes sense. The synth also will give you visual feedback via the program buttons as to what is being edited. Also, all the pitch, cutoff, resonance, ADSR controls, or any other parameter we normally expect to be continuously variable, are all 0-127 steps. I can't remember if the resonance control was limited to 7 steps originally. The upgrade also adds sysex and midi CC capability.
If used with an external midi keyboard with the capability, the upgrade adds velocity and aftertouch.
I also added the chorus speed mod (WELL worth the trouble) to mine, and also rigged it to where it still responds to the PG-200.
Mine seems to be bug-free at the moment, and if you contact Murray at Kiwitechnics, he is VERY responsive to getting bugs fixed as they are found. I found an arpeggiator bug in an earlier version, emailed him, and within 36 hours I got an email from him saying, "Try this one (software upgrade), and let me know if it works for you."
No, it isn't cheap, but it is well done. Remember, price doesn't always coincide with value. I'll put it this way: Once I had a customer bring me a Belles Model One power amp to rebuild (If you haven't heard one, I pity you). The bill was going to be in the $500 area (due to some heavy-duty power supply parts and all new output transistors), You could've bought another one used for less, assuming you could find one. I thought the owner would say no, because it couldn't be done cheaper. He grinned and told me: "Tell me something I can get currently for $500 or less that sounds better than this?" We both knew the answer was "Nothing". He told me to please get right on it.
Point being: If you already have the synth, what are you going to get for $236US that is better?
I would consider making a demo video, but my polyphonic playing skills are weak, so it would be limited to: It can do this, followed by an edit and a really short passage. But, even at that, it would be a REALLY long video to go through everything.