The Pro flash head offers a slower flash duration compared to the Action head but it is faster compared to the HS head. At full power on an ELB 400, the Pro head offers at t0.5 a flash duration of 1/1200th second. For Still-Life and portraits or where the subject is not moving, this is a fast enough flash duration for sharp images. But if the subject is moving then this flash duration will not be fast enough to stop the motion of the subject at normal flash sync shutter speeds, i.e. at 1/250th second or below.
The Pro head can be used in Hi-Sync mode with the latest EL-Skyport Plus HS transmitter, but there will be quite a bit more gradation in the image compared to the HS head, discussed below.
The maximum shutter speeds and the gradation will depend on the camera used.
Large sensors, with mechanical parts for the shutter and the mirror, as well as the camera firmware and the chosen shutter speed will affect the results. Mirrorless cameras can handle Hi-Sync very well.
If you don't shoot action and only want to buy one flash head that can work with Hi-Sync to some degree and also create nice sharp portraits, then the Pro head is a good option.
If you want to shoot mainly at higher shutter speeds, up to1/8000s, then you will want to get the EL-Skyport Plus HS transmitter along with the ELB 400 and the HS flash head.
But, if you are investing in this system, we would suggest getting the Quadra HS, excellent for Hi-Sync and the Action head for fast flash duration. This will offer the best of both worlds, depending on the the situation.