not sure about them, although i might say that as i'm fairly comfortable looking over cars like this myself
i think you get a HPI check in with the inspection though (?), which is handy
last time i had one done (fair old while ago now), the guy was quite thorough and it was worth doing imo; i think i 'saved' the cost of the inspection by being able to haggle the cost of the car down due to the issues he'd found
as with any inspection, there's a limit to what you can look at without borrowing the car and putting it into the garage for a couple of hours to have a really good look at it. with that in mind, there are still things that any relatively casual inspection could miss - there's still an element of luck of the draw