Some people may disagree with me here and I of course respect everyone's opinion. I'm not a huge fan of spiking up a spar with just a lanyard and part of that is simply what I as a climber am comfortable with. It's a matter of having that second tie in and not relying on just a lanyard for me at least.
If I can get a tie in above first I will. If not, what I typically will do is cinch my climbing line around the trunk (either just clip on to itself with carabiner or use a knot), and then advance that cinched climbing line up the spar with the lanyard. Can even advance both at the same time by leaving some slack in the climb line and just holding it with the lanyard. If you do it right you should be able to move just as fast and efficient as you would with just the lanyard.
Three primary reasons I like to do this.
#1 In case of emergency where I may need to make a quick bail out.
#2 If I slip or gaff out, the climb line will tighten and catch me so I don't slide down the trunk.
#3 The added safety of the second tie in.
To some this may sound like more work but I don't really consider it to be. I've spiked up spars with just a lanyard before. Doesn't really take anymore time at least in my opinion.
I'm not saying I'm right either, but I can understand not being totally comfortable on spurs to the point of running up a 100 ft spar like nothing because I do more pruning than removals so do not have a need for spurs on a regular basis.
Aside from that, you need to get comfortable on spurs and have confidence in your ability to climb with them in my opinion. That comes with practice. Practice outside of the job, so you can take as much time as you like trying different things and getting the feel for it.
Also
@treesap when you talk about spiking down, do you mean in between cuts? There's different things and ways to go about it where you can descend on your line and then retrieve your line without actually having to climb down on the spikes, which also saves time and is less stress on your joints. My buddy and I took down a huge pine this past weekend and he climbed, and he had this cool thing that he put around the spar and then put his climbing line through and he would descend to where the next cut would be and we were taking large pieces, and he was able to retrieve his rope from above him. Not sure what the name of it is, would have to ask.