Not too sure that there are any huge advantages in using an inline lead for barbel Peter. The perceived wisdom regarding inlines was that as the link left the lead in the rather unique way it does, then as the fish moved off with the bait/hook in it's mouth, there was a more direct contact with the weight of the lead when the link straightened, resulting in a more successful self hooking ratio. In my opinion, that effect is marginal at best.
There are several ways of setting inlines up, which obviously alters the way they perform. If you are using the type of rubber/plastic insert that allows you to pull the swivel firmly into the central bore in the nose of the lead, producing a virtually fixed lead, then you do of course have a bolt setup....and a short link (2" to 8") will then pretty well insure self hooking.
If you use the type of bore liner that leaves the swivel loose in that larger end bore, then you supposedly have a running rig situation. In my experience, the friction caused by that long bore means that in reality, it is still pretty much a 3' twitch type bolt rig
Come to that, in situations where there is any noticeable chod on the bottom, then very few rigs of any sort are genuine free running rigs...certainly not guaranteed to run on each occasion. I have modified and adapted quality lined single leg rod rings (8/10mm dia) to use as running rig rings...and STILL had them bunging up and refusing to run occasionally, when used on choddy bottoms (though admittedly that was lake fishing).
One thing to be very careful about when using inlines (particularly heavy versions) is to do with the fact that the hook link exits the lead at centre front. Like any streamlined lead, inlines dive nose first straight towards the bottom as they hit the water...and in shallow or even moderately shallow water a hard bottom (such as gravel) can result in a hard contact. Because the link is wrapped around that nose end on impact...then obviously it can do some serious damage to that link. Admittedly, that is much more noticeable on a long cast, because of the increased speed the lead is traveling at on entry....but worth a thought whatever! The point is, you can set things up to achieve that same bolt style effect with any type of lead you wish to use, so there are safer ways of achieving that.
Give it a try, see what you think.
Cheers, Dave.