I've played a Harpsicle as well as some others. They've got quite decent tone and volume for their size and price. If your budget is really tight, or if you want a really compact/lightweight harp that you don't mind receiving mild abuse, they're a good option.
If you can spring the extra $ for the Sharpsicle (sharping levers on C & F) or Flatsicle (sharping levers also on the B-strings tuned to B-flat) you'll have a broader range of keys in which to play without messing with re-tuning.
The tension on the strings is fairly low. You could get away with retuning a few strings up 1/2 step to change keys if you can't afford the levered models - but that's more hassle. (DON'T re-tune the entire harp - just sharp the particular notes) Another detail about the low tension on the strings is you'll want to use a fairly light touch. Plucking with the force normally applied to a big concert harp won't work so well.
I second Molly's comments about the Ravenna - and I'm not associated with Dusty Strings nor any other commercial harpmakers. They are really quite nice instruments, and well worth the price. Dusty has come up with some innovative manufacturing methods to turn out a good instrument less expensively.
Another small harp that has surprisingly good sound is the Triplett Christina - but that's bouncing up into the over-$1000 price bracket. If size is your concern rather than price, consider that option.
If you're even middling competent with basic woodworking, consider the MusicMakers kits. I've been playing their Shepherd lap harp (22 string) for a while, and constantly get compliments on its tone. I highly recommend any of their kits - they are well designed and are relatively foolproof.
As for the limitations of a small 19-string harp, consider this: most melody instruments have only about a 2-octave range. That's 15 notes (diatonic). So at 19 strings you've already got a half-octave more than that! Granted, you may not be able to make it sound like a big concert harp- it's a different instrument altogether. You don't hear someone saying to a violinist "so when are you going to get rid of that little instrument & move up to a full-size Bass?" Different instrument, different techniques to get the most out of it.
I do suggest that if possible you find a way to listen to the instrument you are thinking about buying (live, not recorded) to see if you like the tone. Also remember that harps usually sound MUCH different at the position of the player compared to the sound that goes out to the audience - so have someone else play it while you stand a few feet in front.
Have fun in your harpquest!