Personally - I have not used PCs and I do own a CT. I can test myself year round on the CT - and I use this b/c each test is measured on the same course and it's as accurate as you will get with the exception of going to a lab. In my opinion the CT is like your own little testing lab right in your own house.
I am big on train, train, train, then test. It's the only way to measure improvement. Same conditions, same course, etc. Consistency when testing is critical.
I would imagine that Frank has some way to test yourself on the PCs but like Mike Plumb said, if you ride indoors, the CT might be better for you.
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2017 USAT World Team Coach
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Coaching Triathletes since 1992.