I built a house last year and used them. I did not want a bouncy floor either and if designed right, it won't be bouncy. I sized them myself on the plans from span tables available. I am a mechanical engineer but didn't try to do real calcs as that is done in the span tables. My builder thought I over-sized them so we ran it by the civil engineer at the supplier and he agreed with me. So, left to some builders and others, I could see how you could end up with a structurally safe but bouncy floor. The floor is flat as a flitter (that might be a local saying). I am happy with them. If you use them make sure the builder installs "squash blocks" at all load bearing points above which is typically the ends where exterior walls are and other interior load bearing areas. They should not pass framing inspection without the squash blocks. They are readily available in stock lengths and delivered faster than floor trusses. The negative compared to trusses is running duct work, pipe, wire, etc through them. I would not frame with 2X lumber again for floors.
I will add that mine are above minimum allowable in the tables. They are 14 and a fraction tall, on 16" centers, with a large LVL beam at midspan and span from end to center beam is about 16'. The floor is glued and screwed with 3/4" Advantech subfloor. We have been here about 18 months now and the other day my wife commented "have you noticed there aren't any floor squeaks anywhere". The house we moved from was 2x12 joist, glued and nailed plywood subfloor with hardwood, built in 1991 and had floor squeaks lots of places.
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