i use a lexicon lambda and have for the last three years.
it was a good interface to learn on, and will introduce you to some of the basics of real recording. lexicon includes there world famous reverb plugin (pantheon) which i have used many times.
if you dont know, the reverb plugin is particularly helpful when you have really DRY tracks (like recorded in a vocal booth, or treated room) because it then allows you to basically create a "fake room" that has the amount of reverb that you want it too, and you can change the size, the echo, the delay everything of that room by a simple slider.
it sounds complicated but its really a great thing when you learn how to use it.
after a few years i treated my studio acoustically, and the lexicon lambda records tracks almost and i do mean ALMOST crystally clear, its only a few steps off a "pro" sound. But thats also with my practice on the unit for the last 3 years. so i have somewhat developed my sound when using them.
i can only comment on the lexicon lambda because thats what i use, but...
basically, i would say, lexicon has...
-good quality preamps for a lowbudget device, im sure there the same on the omega
-good device to start on
-CAN sound great and make great recordings with practice, and hard work
-well built, long lasting, sound-satisfying
but the bad thing is...
-in 1-5 years, if your still recording and looking to continue improving your recordings, you are most likely going to have to update your gear, as a lexicon is only going to take you so far.
of course theres many other really good things, and some other bad things and limits of the unit itself.
but i cant complain, people have always enjoyed my tracks and said "wow.. it NEARLY sounds pro!!!" some even say it does sound pro, and thats always nice. i would call it a "high quality demo" sound.
you should buy it if its going to suit your needs to record.
if all you need is to do a vocal track, or a guitar track at a time. this unit will work great, and will sound better and better as you learn how to use it.