There are very specific advantages to using PHD Predeflected Holdowns over the HAD type – e.g. using screws rather than bolts when fastening the holdown into the concrete foundation. 

Alignment:  bolt holes need accurate alignment, while screws can be drilled without any alignment at all

Tools:  Screws only require a drill and the proper bit, while bolts need pilot hole drilling, counter-torque tools (e.g. rotating one end while keeping the other end secure takes two tools), and often a mallet of some kind to properly fit the bolt into the pilot hole. 

Access/Interference:  Having to deal with two sides of a bolt is a large disadvantage.  Screwing in an anchor requires no access behind the post.  Also, bolt head and/or nuts can potentially interfere with other elements, like doors or windows.

In general, bolts are difficult to install and require too much time and effort.  This is the main advantage of PHD Predeflected Holdowns.   

Finally, just as a quick note to contractors, PHD Predeflected Holdowns may be raised off the sill plate, however design considerations must be taken for the increased deflection values.