My zip ties are from a home improvement store, the same tube packaging that everyone is recommending. My impression is that they are of higher quality than regular zip ties - they feel a bit thicker and the latch seems quite sturdy.
The system itself is elastic so I don't think you can claim no tension loss if you've had the mod in place for months. I don't doubt though that there will be many of you who make it through the lifecycle of the card without ever having to change the zip ties, but I did want to share my store as a caution. In my experience the system can be finicky.
I'm curious if anyone using one of the square corsair blocks is seeing the same issue?