Have cast the 15' ONE side by each with the Highlander 15' 7-9 recently. The ONE is full flexing, progressive with a stiffer bottom third (but not STIFF). What sets the ONE apart, even though it bends easily it only bends so far then you find the power in the rod. The ONE WANTS to be flexed relatively deep. When you do, good things happen and they happen fast. The action is fast just not stiff. (15' METHOD has a similar bend curve but is faster and stiffer throughout, yet throws the same lines.) The ONE has OODLES of feel, letting you know everything going on from start to finish. Water anchored casts are exceptionally easy...you could almost say that it was designed into the taper. Temperamental is also a word I would describe the 15' with. Cast the rod like a fast action stick that is much stiffer than it is and you will smile. Big toothy grins. Treat it like a full flexing rod (and it does feel full flexing at first) with slow, plodding movements (you know- the kind you track with a sundial) and prepare to frown. So get a little giddyup to your step!
The 14' ONE flexes deeper than the 15'. Yet retains similar characteristics, just powered down. A lot powered down. Easier and less temperamental. 7/8 Nextcast heads are what my hands prefer. YMMV. You have a rod that feels in hand like a 13'r yet you get all the benefits of being 14'. This thing is a sweetheart. As long as my fishing distances are consistently 70'+ I wouldn't hesitate to use it on basin A runs. Or take it to places where fish over 10#'s are the norm. Let alone to tackle toads. What I am saying is the rod is suited for tons of fun regardless of what scaled critter latches on and interrupts your casting enjoyment. At one point in time the 9140 was the .3006 of spey casting on the west coast. For many reasons shorter rods and ever shorter (and heavier) heads supplanted it. This stick at least makes the 14' rod relevant to the debate again.
The descriptions about tracking and recovery are all true. If your casting is sound you will see the laser straight flight.
While my hands on experience is with the 14' and 15' models, hearsay also speaks (from those I trust completely, even with my life) the 8136 may be the jewel. Pick ONE and have fun...