The debate between dynos is fervent. The folks at Hirsch do not generally like the inertia ones; there are other options between those two. Most dynos are either inertia or water based though.
It's been quite wet here too. During the day a 100-200 kph test would be irresponsible, if not impossible, due to traffic. But tonight it is supposed to rain again. (It's been raining for nearly 2 weeks straight here. Perhaps not as bad as snow, but it makes high speed especially risky.)