I ran across this one myself when I was testing some modifications to the aset layout (which oddly enough eventually worked into colemak anyway) a while back. The readout is pretty, and switching keys is real nice and easy. The layout creation is amusing but questionable. Overall, I decided that I liked the codesharp layout tester better.

site:
http://www.codesharp.co.uk/dvorak/

Edit: As a side note, ignore the ddvorak (developer's dvorak) at the codesharp site. Calculations get screwed up where AltGr and dead keys are concerned. For some reason they don't count for the "% of keys needing the SHIFT modifier" amongst other problems. So ddvorak (which shifted all numbers to AltGr, and most punctuation to deadkey combos)  tends to gain an unfair advantage in that category. This might have been alright, balancing against having a higher keystroke count, but the weighting is... odd. For example, put "1234567890" as the text and run the comparisons. Ddvorak will still beat out the regular competitors (qwerty, dvorak, colemak), despite having double the number of key strokes. Try it yourself and you can see how it gets there, but it is still odd.

Edit2: For those who are interested in testing your own dead keys and AltGr layouts, the code for the ddvorak (http://www.codesharp.co.uk/dvorak/DDvorak.aspx) layout is as follows

###()_#**+*N;##*R
#',.pyfgcrl
#aoeiudhtns&
*L|qjkxbmwvz
*L

###APYFGCRL
##OEIUDHTNS
##QJKXBMWVZ
,

###"\\#~!-?
####=#*#}{:^
######@%#$£
*A

##[]###789
##</>##456
######0123

Everything else is pretty self explanatory. Have fun.