I have experience of the RB300 and own an Ittok. Never having heard them side by side nor in similar context, it's hard for me to, directly, comment on their relative merits.
However, I do think the Rega arm is brilliant; simply made, quality product, at a bargain price. The one-piece casting is genius; I wonder if even Roy Gandy expected to sell as many as he has. A bit of tweaking can take it to even higher levels of performance.
The Ittok, on the other hand, is different; a much higher quality of finish and material. It is clearly a more expensive product. People used to use the term "camera finish"; the Ittok has it in spades (especially in black). 400+ for a good example; I think it's worth it!
By the way, mine has actually been in storage for 10 years. Changed it for an Alphason HR-100S, another excellent arm. I am now on an SME IV and while SME always receive laudits for their finish I think the Ittok is right up there.
I don't really get the significance of the made in Japan or Scotland issue; fine if you're scottish and you want to support home industry but the Ittok was Made in Japan in the best possible sense.