Which U-BLOX?
I have found USB GPS units based on the the U-BLOX 7 to be common & reliable (although U-BLOX seem to regard it as obsoloete), some Windows driver issues in the past, seem better now, but great on Linux. VK-162 & VK-172 units (VK-162 often called "G-Mouse"). Generally about 5m horizontal drift, but occasionally up to 25m variation.
When you're getting a VK162 or VK172, it may be worth verifying with the seller exactly which variant of the chipset you're getting. I have a few old VK172s that are M7, and got a new "M8" based 162. Yes, it an M8 but it's the M8130 which is a low cost version for the Asian market, doesn't have support for Galileo, and only supports two simultaneous systems. The M8030 does support Galileo and probably supports 3 simultaneous systems. Just something to be aware of.