On this occasion it was being used as a deep drop rod.

Those interline Diawa’s are designed I think for jigging, although a mate used to strayline with them successfully for snapper with an SL20.

Thing with a marlin is 600 meters or so is probably  going to leave reel real quick so could generate a lot of friction on tip, the point of entry to blank, or in between. Also needs to be stiff enough to set game hook in lure, and absorb strike.. those interlines are also graphite from memory. Going bang on a marlin might be regretted.

Fish Addict wrote: How do you reckon this rod would go as a game rod BFB.  No troublesome guides to deal with.   Having said that the use of windon leaders could be an issue due to the internal diameter at the tip.  The model in the pic is rated at 50-80lb. On this occasion it was being used as a deep drop rod.

You are quite correct that they never took off for game fishing however I don't think they were aimed at that market.  I'm not exactly sure what market they were aimed at, but whatever it was the punters weren't interested.  This model is not a jigging rod - not parabolic.  Yes the are graphite.  

The question about increased friction with these interline rods is something that fishos have often mentioned as a negative.  Game rods typically have four guides and a tip.  That distributes load on the line over five point load locations.  Interline rods distribute the load over the hollow length of the rod.  Is that more load at any given point along an Interline rod than a point load at a guide?  Too hard for me to work out.  I've read a little bit trying to answer my own question without substantiation either way.  What I did find out however was interesting.  Most people seem to think the max load on a game rod is on the tip.  That's incorrect as the tip is generally pointing in the direction of the line.  The max point load is 2 or 3 guides back as I understand it.