Trekkers aren't ideal, but they work, -I'm speaking from personal experience here.
With regards to Trekkers interfacing with FKS180, there are a few things you may wan't to watch out for. Firstly due to the high heel piece, you may not be able to get you heel all the way down. This would only really be an issue on long flat approaches. Note, I haven't used Trekkers with an Pivot heel piece, but I have used it with a PX heel piece, which is equally high. Infact the PX heel piece is marginally higher than the Pivot heel piece, so there is a chance the you may be able to get your heel all the way down. But down quote my on that as I've never tried to run Trekkers with FKS/Pivots, maybe someone who has would be able to confirm one way or the other.
The second main issue with running Trekkers with FKS180, would be engaging the brake on the Pivot heel piece . Due to the nature of the break on the Pivot heel pieces, the rail on the Trekker which is designed to engage the break, is not low enough to engage the break. In short it the Trekker doesn't engage the break on Pivot heel pieces. This can be easily combated however by winding tape around the rail on the Trekker so that the break is engaged.
Sorry if this is hard to read, I've been up 19 hours now,
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Joey -Formerly *III.JVD.III*
I post from mobile the majority of the time, so if the above is incomprehensible, I apologize.