Thanks for sharing your experiences with these tubes. It saves the rest of us a lot of time and expense ordering materials to see how they work.
I would add a note of warning. After plowing ahead despite Roger Caffin's warnings, I've had a number of issues develop with pultruded tube and even solid rods. They have a nasty tendency to split, and sometimes even fracture across the grain. My purchases were from Goodwinds kites; however they sell Avia Sport, which I believe is sold on many of the sites.
I don't know if the pultruded carbon on the Kites and Fun Things site is any better or not, and know nothing about how much the quality of the resin bonding materials may vary. Kind of a repeat of where I was at a number of years ago with the quality of silicone coatings on silnylon. Ugh! Also note that a number of pultruded tubes sold as .240 O.D. are actually .236 to 238" O.D. and too small in diameter for a .244" I.D. tube. For purposes of comparison, Easton poles generally use ferrules that are 2/1000 of an inch smaller in O.D. than the I.D. of the main tube. I believe looser ferrules greatly increase incidence of breakage.
In any event, there are some alternatives to ferrules made from the stock pultruded tubing. For the larger diameter tube you mentioned first, there is Easton .344 ALU tube, available from Quest Outfitters and others, that can be cut into ferrule lengths. Last winter/spring we posted on a long thread from an OP about the larger carbon tubing. At that time, Roger posted some reservations about how strong it could possibly be given its weight. I ordered a few pieces from K&FT to look at, and they indeed are very thin-walled.
For the smaller diameter tubing you mentioned, Easton makes its Injexion arrow shafts in a .240" O.D. that might be sturdier than stock pultruded tubing. (An earlier post from me was about using the heavier .244" O.D. Injexion shafts to make ferrules for .245" I.D. tubes.) Easton claims that although the Injexion shafts are pultruded, they use a proprietary process. I don't think that Easton would manufacture arrow shafts as fragile as stock pultruded ones, and so am willing to bet on their shafts being superior.
There is one more thorny issue with this ferrule business. The ferrule must be at least as stiff as the main tube, or else when the tube is bowed, there will be an angle created where the outer tubes meet over the ferrule, and greater pressure on the lips of the outer tubes that invites breakage. More often though, the ferrule can be significanly stiffer than the main tube, unable to flex as much as the main tube, and thus placing greater pressure on the main tube at the lip of the ferrule inside it. So not only do we have to be thinking about the fit of the ferrules, we also have to look at their flexibility compared to the main tube. Fortunately, most of the arrow shafts are rated in terms of "spine," indicating their flexibility in terms of fractions of an inch deflection with a standard weight and span. So, it is possible to know if and how much stiffer the ferrule is than the main tube.
Please note that Carbon Express has a product named "Bull Dog Nock Collars." They are small red anodized aluminum rings, intended for the nock end of arrows, that fit over the end of carbon tubes to resist breakage and split ends. They are much cleaner and lighter than rings made from cut tubing, and come in two sizes, 250 and 350; and as best I recall, the 350 fits the end of SkyShark P3X tubing, and may fit Victory VF V6 400 shafts with some lubrication.
Hope all that is of some interest to the carbonites amongst us.