Yes they are safe to climb on. Are you sure they are shorter? I don't have the directions in front of me, but aren't the toss directions longer? I thought samson has you make the first mark at 1 fid length (which is about 21 rope diameters) and toss has you make that mark at 24 rope diameters.
The first time I tried splicing double braid, I used the New England Ropes directions (posted on their website) and had no difficulties at all. Most double braids are very easy due to the loose weave of the rope.
I did buy the wand and broke it on the very first splice I tried with it. Was trying to splice 16 strand arbo rope and the wand wasn't long enough to do the bury in one shot anyway. I ended up throwing it away (after taking out my frustrations on the stupid, overpriced thing) and went back to using a coat hanger. For the last 5 years I've found it easier to simply order the 16 strand already spliced, but double braid can be done quickly and easily even with well used rope. And I'm not a splicer by any stretch of the imagination.