I owned one a few years back, great boat for everything from crabbing to deep water stuff. Mine originally come from Karratha, so probably saw a few creeks. Mine had a 70 Yamaha on it, very economical. Don't draw a lot of water and don't need much to get them on the plane. Can be a bit wet, but hey, it wasn't for me behind the consul. 

 Spent a lot of time in one in late 90s when they seemed to be everywhere 

Mate had one and we pulled pots every morning for a couple of seasons and out to the 40s bottom bouncing quite often.

was a wee bit bigger than 580 from memory thou

never really felt unsafe...always felt wet!

just be careful in a decent swell cause they don't like being anything but square on to a decent size swell (both into and on a following sea, suggest you don't turn anywhere near side on mate......suppose same is case for most small boats but seem to remember thinking with their shallow draft and narrow beam it wouldn't take much to go over....).

all that said...some of the best memories I have is from one of these!...and we/I was pretty brave (dumb and fearless) back then and we were out often in some ugly water and we never came unstuck...

 We have an old one. Not sure if they have changed the shape. Great in close, but they bash like nothing else.

Once the issues were sorted with my UB 520 it was a fantastic rig ( I ended up with a yam 80 4st on it) I pirchased mine new from the boat show in 98 and it subsequently started to fall to bits before they found out some idiot had forgotten a couple of layers of fibreglass diring the build.....I was basically out fishing in a layer of jelcoat lined with some fibreglass.

BUT when they replaced the hull....I had thousands of hours of pleasure from th UB, really seaworthy, low maintenance, and tough as nails.

but " tippy" to walk around in, but a soft wet ride ( anyone who says they bash hasn't heard of the trim switch) 

recommended.

 Boat show special from Fremantle Yamaha--was before the "-9" went on the front of the WA phone numbers , so would make it around 95? Had a 70hp yammie on it , I loved that boat. Basic open CC, added underfloor fuel, and made a little insulated box in the access space behind the CC, and also built a big glass icebox with seats on top that pegged into the deck and could be lifted out. Only sold it when I bought my own crayboat, money was a bit tight. Seeing what they go for now, I could have stuck it in a shed and then sold it 15 years later, $ would be exactly the same as I let it go for in 2000.  Anyone who reckons they bash has either a) never owned a 16ft tinny, or b) come down from a much larger, heavier deep-vee hull

As you probably realise, they are built on a traditional longboat design used all over the world through the tropics. They really don't need a lot of HP to get them going, but the long and narrow design has it's own peculiarities. They are quite sensitive to trim, both fore and aft and laterally. Getting up on the plane with a few people on board always meant starting trimmed right in then trimming out to suit. This is very easily fixed--just fit a foil to the leg and the " problem" goes away. Don't listen to any one who weighs in with a " me mate had one on his Trailly and it made it dangerous downwind" contribution. On these hulls  ( both the 19 and the 21) they just work, period.  Much less or no input needed on the trim between still and planing, depending on the load. Laterally, as they are quite narrow, it's easy to have a list up if people decide to sit on the gunwhales. it never, ever felt unstable, you could leave it roll side on, not a problem. 

I found the ride generally quite dry--it IS a CC, after all. Beautiful into a short slop or a big swell, very soft-riding. Never had an issue downwind, but I guess you can always get someone who drives like  a fuckwit , has the boat bite him, then blames the boat...ran it down a fresh southerly coming back into Kalbarri in summer many times, sometimes loaded with crays, never a bad moment. Was used as a tender for a while when we had to moor at Jacques or the Bluff when the river was closed, which meant heading out the mouth and south in the dark, loaded with bait, maybe a spare pot or two,  coming back with the catch.

Negatives? Lack of storage space. You have no side pockets. There is a well with lid up the front, the console, probably with a seat box in front(?), and the rear compartments,which are wet, ie, drained by bungs. You just need to be economical with what you carry.

A young bloke up here has a 520, (shortened 580)fishes by himself a lot--I see him go past in a bit of slop and it always looks to be riding beautifully.