i have owned 4 of them: the Specialized ? Pro, the Cateye and 2 Ciclos.

the Ciclo is by far the best and is basically as accurate as my expensive Sunnto mountaineering altimeter, but they're not cheap (the C414M w/o computer is about $100 (not so sure) & w/ computer connection is about $150, the HAC4 with HR monitor is around $200 - and this is in Germany so could be more in the US - not sure?)

the Specialized was my first and i found it pretty accurate.

i also have the Cateye and after having had the Specialized and now the 2 Ciclos, i use it only on my commuter bike and rarely use the alti function. the alti is very inaccurate compared to the others. most of the time is is basically useless - almost just a novelty to have it displacyed.

with the Cateye i have 3 problems:
1) it is somewhat inaccurate meaning at the end of a 500m climb it may say anything from 410 to 590m difference in elevation.
2) the ACCUMULATED vertical is REALLY wrong. both the Ciclo and Specialized to an amazing job - i.e. ride up and down and the amount is a) the same for different computers for the same route time and again and b) usually matches with what i expect from a map. the Cateye sometime will say i've climbed 3000m when i've climbed more like 400 - i know what the difference between 3000 and 400 feel like!
3) from day to day it always gets funky readings. yes, the barometric pressure changes every day, but not THAT much. one time it was 100m too low EVERY day for 2 weeks - it's just not possible that the pressure rises that much every day.

anyway, i think the Cateye is fine for speed and other stuff and i like their bike computers, but the altimeter is just too inaccurate. if you just want to have a basic rough estimate, then it is fine. if you really want to know the accurate elevation and/or want to track vertical climbed or descended, don't buy it.

not sure if you can get them in the US easily as they come from Germany, but the Ciclos are the best. i was also satisfied with the Specialized (before i had the Ciclos).

if you can find it, i'd recommend the Ciclo C414M - either w/ or w/o the computer connection. it has a wireless sender which works well, the only problem is the 2 batteries in the sender/receiver must be replaces about every 16 months or so...