Buying Pro's Hydraform TT handlebar and Synop Al Clip-On aerobars as a set like this saves you a tenner over separates. The handlebar is oversize, with a 31.8mm diameter and a width of 42cm centre-to-centre (oddly, it's listed as 40cm).
As you'd expect, it's very stiff. Brake cable runs can be concealed within the handlebar, although the 90-degree square bend from handle to bar makes installation a bit fiddly. The 'wing' shape of the bar is slightly more aero than a rounded tube. However, the position of the aerobar armrests makes any talk of aerodynamics a moot subject. It's too high.
To be fair, plenty of clip-on aerobars are just as bad, but not all – my ITM Ultra VIP aerobar (which costs about the same as the Synop Al Clip-on) has armrests just 1cm above the bar top; the Synop armrests are 4cm above the bar. Sitting up into the wind is about the worst thing you can do on a TT bike. I like the handlebar, which looks the business, and the S-bend of the aerobar is comfortable. But I'd only race on them if I had a stem with a drop of 30 degrees or so to get the ride height down.