For smaller vivs a compact is really the only option, where a conventional tube would be too long and a MV too big and hot. Compacts have a problem though as the tubes block each other, so a good reflector is essential to get the most out of it. Of all the makes the Arcadia is generally reckoned to be the best, and the linear arrangement of the tubes, rather than the coil shape some brands use, helps to minimise the blocking. They're also said to be good for 12 months rather than 6 like most cheaper ones.