Hand alternation
Hand alternation vs same-hand rolls
Dvorak achieves significantly higher hand alternation in the expense of higher same-finger ratio, imbalanced hand load, heavy strain on the pinky, and less roll combos (multiple keys hit on the same hand with one comfortable movement). Colemak wasn't designed with hand alternation as a top priority. In fact many modern alternative layouts (e.g. Capewell, Maltron, Arensito, Qwerak) do not try to maximize hand alteration, e.g.:
Arensito design: "I finally wanted to maximize the probability of having two consecutive keystrokes happen next to each other. This keeps the fingers rolling and increases the typing speed (Dvorak was wrong!)." (source)
Qwerak design: "Slightly decrease frequency of hand alternation (e.g. swap S and O) where within-hand rolls across adjacent surface keys can be less tricky than inter-hand alternation timing." (source)
Capewell design: "Maximize the use of 'combos,' i.e., multiple keys hit on the same hand with one comfortable movement" (source)
Putting all the vowels on one side means that you need to place vowels on the index finger, and thus highly increase same-finger ratio, or be forced to put common letters in weak positions. I've found that same-finger typing causes slowdowns more than any other factor.
Fraser Street comparison
Source: Computers and Automation magazine, November, 1972, pp. 18-25. (Dvorak layout advocacy). This text is made up almost entirely of one-hand words on the QWERTY layout.
QWERTY
left hand underlined
Fraser Street was in West Everett. Westward of Fraser Street the great vast sea. Awed, we gazed seawards, attracted by crested waves which raced and ebbed. Children were scattered on the beach edged and strewed with seaweed. They waded in water as the sea surged in and retreated. They bagged crabs as eagerly as beavers saw trees. Brave crews, seafarers in fact, steered sea craft far away. The site of Fraser Street was not overrated.
Few vegetated in Fraser Street. Nobody wasted time abed. "Acts test the breed," was ever the sacred adage. Varied crafts and trades were represented. There was a caterer, a barber, a weaver, a cabaret, and a garage. Attracted, we started to see several scenes. We were greeted as friends.
The barber catered to a varied trade, representing diverse careers and different creeds. Saturday drew the best crowd. All were seated, relaxed, aware of fewer cares, less fagged. There we saw a few starved tattered beggars who bragged of "bracers" served at cafes after a wee meal of beef stew and cabbage. A better fare was reserved for those reared on earth's greater awards.
Colemak
left hand underlined
Fraser Street was in West Everett. Westward of Fraser Street the great vast sea. Awed, we gazed seawards, attracted by crested waves which raced and ebbed. Children were scattered on the beach edged and strewed with seaweed. They waded in water as the sea surged in and retreated. They bagged crabs as eagerly as beavers saw trees. Brave crews, seafarers in fact, steered sea craft far away. The site of Fraser Street was not overrated.
Few vegetated in Fraser Street. Nobody wasted time abed. "Acts test the breed," was ever the sacred adage. Varied crafts and trades were represented. There was a caterer, a barber, a weaver, a cabaret, and a garage. Attracted, we started to see several scenes. We were greeted as friends.
The barber catered to a varied trade, representing diverse careers and different creeds. Saturday drew the best crowd. All were seated, relaxed, aware of fewer cares, less fagged. There we saw a few starved tattered beggars who bragged of "bracers" served at cafes after a wee meal of beef stew and cabbage. A better fare was reserved for those reared on earth's greater awards.