Tell me about Tri-Bars

As I said on the 'weekly race log' thread, when I turned up to do a time trial last weekend (for the first time since 1991) I noticed that everybody else was using tri-bars. I have never used them, but was wondering if it was worth investing in some clip-on ones for doing time trials? I'm assuming the aerodynamic effect is worthwhile. I haven't got the money or inclination to have a specific time-trialling bike and the vast majority of the time I wouldn't be using these bars, so I'm not looking for something permanently fitted with gear levers at the end, just something I could stick on before a race and take off afterwards.

My handlebars are FSA Wing OS. They aren't round all the way along, on the tops they are a kind of flattened oval shape without any tape on. I don't know if this is standard nowadays, but I thought I'd mention it in case it affects what can be fitted.

Any suggestions? Cheap is good, by the way. Oh - and is it a waste of time if I don't have gear levers at the end (as judging from last week, I would be constantly having to move my hands to the hoods to shift up and down)?

NB I AM NOT A BIKE RACER

aero bars ought to make you more aerodynamic, but unless you're competing at a certain level, i doubt they'd improve your time/performance as much as training would? i mean, invest in them if you like, but you're not likely to see them pay dividends unless you're already pretty fast

but i'd defer to Hunt3r and cutttty on this one