Get to T2 faster.
Profile Design set out to make a collection of clip-on Aluminum Aerobar Extensions that would give every time trial rider or triathlete the option to be comfortable in the aerobars. Choose the one that most closely matches what you want, then clip on and go. These aerobars are designed to be easily attached to a road bike, bringing you closer to triathlon or time trial bike geometry, but your bike will probably require some fit adjustments before you're ready to go.
The biggest difference between each model comes down to shape. If you're worried about aerobars that make your hands and wrists go numb, the T1+ was created to be a more neutral option. Their shape gives you room to move your hands around to get the right fit, and while still aerodynamic, they aren't as aggressive as flatter styles. If you're concerned with how you might feel at the end of your race, the T3+ offers the most neutral wrist position of the series and gives you a little more room to adjust your hands throughout your ride.
By contrast, if you care less about comfort over the long haul and more about getting in an aerodynamic position, consider the T2+ or the T5+. Your hands will sit low in the T2+, but they were designed with a 30mm rise so that you're not completely stretched out. This year, Profile Design added the T5+ to its lineup to blend the aerodynamic benefits of straight aerobars with a slight ski-bend angle. Expect bars that are the most aerodynamic in the series with just a slight 15mm rise.
A shorter extension length sets the T4+ apart from its counterparts, which could be beneficial if you're hoping to not have to make major fit adjustments to your road bike for race day. The extension shape falls in between the flatter T2+ and the more neutral T1+ and T3+ models, so you end up with something in the middle. Each of Profile Design's extension bars fit on handlebars with a diameter of either 26.0mm or 31.8mm.