Never had one, and I assume VIA C3 will be like other MX chips.
All the MX chips I knew had weak FPUs, but they also had an exaggerated unfair reputation because they were nearly always paired with the cheapest expansion cards, cheapest HDDs, and cheapest RAM - if someone installs silicon/drivers that push more work to the CPU then the system will crawl and that's not the CPU's fault.
To get a fair comparison you need to dismiss the Performance Rating written on the chip (bad Public Relations) and instead compare only the core MHz. Running a 150Mhz Cyrix (IBM 233) against a 150MHz Intel, or a 233MHz Cyrix (MII 300) against a 233MHz Intel, was much more interesting than anything the magazines ran with.
And, overclocking was another area that may have unfairly killed their reputation. I am not saying they overclocked well, but failure rates made me think they may been abused more than Intel chips. Using a P233 as an example: If you stick to MHz then 10% of 150MHz is +15MHz, and apply that to get ~165Mhz total - I expect that 10% increase on stock cooling would work for any CPU. Use the same CPU but this time muddle PR and MHz: You might have said 10% of PR233 is +23Mhz, and apply that to get ~173MHz total - I expect that 16% increase on stock cooling would fry any CPU.