The Trinity series (as opposed to the higher-end Trinity Alliance bikes) are all-aluminum frames. In their competitive set (bikes under $1900) you'll find QR, Felt, Cervelo, Trek and Fuji, and these are also all-aluminum.
Priced at $1750, this is the Giant you want, if you're choosing between the two Trinity models. The frame has rear entry dropouts, aero seat tube and post, sensible tri geometry and is made in what might be the premier bike factory in the World. When you think of the most august bike brands in Europe, like Colnago, and the most respected brands in America, like Trek, companies like these are very picky about the strategic partners they choose. And Giant is such a partner.
Look at the Trinity Advanced line and you'll see what Giant's capable of building. But Giant's real strength is in its ability to churn out low and mid priced bikes, bike after bike, and have them be perfect, and priced dynamically. Enter the Trinity 0.
The genesis of this bike's geometry was a trip to a F.I.S.T. Tri Bike Fit Workshop by the then-product manager of Giant's road bikes. The geometries that came out of that experience found their way to the Trinity Alliance, and then to the Trinity. The seat angles are mid-steep at 78°, and the head tubes are reasonable lengths given the seat angles. These Giant bikes are much easier to fit aboard than the all-carbon TT bike that Giant made prior to the 2010 Trinity Advanced. These Trinity models are easy bikes to ride.
Thematically, the geometry of the Trinity is in between two styles. It's not as "long and low" as the bikes made by Cervelo, Felt, QR, and Kestrel, and it's not as "tall and narrow" as the tri and TT bikes made by Cannondale and Scott. The Trinity models are a nice middle ground that'll fit a lot of riders.
This bikes sells for $1750 complete, and features a Shimano 105 gruppo (including brake calipers, and with an Ultegra rear derailleur), with some cross- or down-specs. The cranks changes from a Race Face Cadence crankset (2009) to an FSA Gossamer Mega Exo (53/42). Tektro brake levers become "Giant" brake levers (tho I believe they're simply Tektro rebadged). It's got a set of Visiontech clip-ons as the aerobar and a no-name but, one assumes, acceptably functional wheelset.
A nice feature of Giant's TT bikes is a seat post that has the hardware mounted on a set of "ways" that can slide a centimeter fore or aft from center (it is pictured adjacent). This means the bike is easily set up to ride at 80° or 81° if that's the config that floats your boat.