Holy crap this is petty. I think we can all agree that 300% of...

Holy crap this is petty.
I think we can all agree that 300% of something is 3 times that thing.
The confusion arises in that it's a 300% improvement - which means it needs to be added on to the original.  Otherwise, a 100% improvement is no improvement at all because 1 x 100% is still 1.  Using that logic, a 50% improvement would see a decrease in effectiveness (1 x 50% = 0.5), which makes no sense, because that's actually a reduction.  So that can't be correct.

So, if the improvement must be added on to the original:
1 with an improvement of 50% = 1 + improvement of (1 x 50%) = 1 + 0.5 = 1.5
1 with an improvement of 100% = 1 + improvement of (1 x 100%) = 1+1 = 2
1 with an improvement of 200% = 1 + improvement of (1 x 200%) = 1+2 = 3
1 with an improvement of 300% = 1 + improvement of (1 x 300%) = 1+3 = 4

Now, whether the marketing gets it right is another issue.  I've seen it mentioned that the wand provides 3x results.  Which would be 300% results - but is different from 300% improvement on the original results.  It's certainly an improvement on the original, and the results are 3x the original, but the improvement component is only (300% (total) - 100% (original) =) 200%.
However, this thread probably shows why the marketing has discrepancies - because people get confused between the two.