The Alpha Omega is not a "bad" seat *but* there are many more seats in the same price range that will give you more bang for your buck. Many Costcos still carry the version of the Alpha Omega with a 40 lb. harnessed weight limit and a notoriously low top harness height setting that most children outgrow by height WAY before they're close to 40 lbs. (chances are good that your 3YO is already too tall for it), and it does NOT function well as a belt-positioning booster either ( see http://carseatblog.com/906/alpha-omega-elite-eddie-bauer-...)
If your 3YO is forward facing, the Graco Nautilus (about $150) or Evenflo Maestro (about $80) would be good choices that would keep your child in a 5 pt harness until he/she has the size and maturity for a belt-positioning booster. Both convert to decent boosters after the harness is outgrown - the Maestro is a bit shorter and will be outgrown before your child is ready to use the seat belt without a booster, but since a good basic booster like a Graco Turbo Booster can often be found for $50 or so, this isn't a big drawback and the Maestro could be handed down to the 19MO)
For the 19MO - the Graco MyRide and Evenflo Triumph Advance are two convertibles in a similar price range to the Alpha Omega but with much higher height and weight limits that will fit your LO much longer than the Alpha Omega. Hope that helps!
BTW http://www.car-seat.org is a great resource - many regulars on their forums are certified child passenger safety techs and are very helpful and well informed