Well for the what its worth department. I have owned a pair VTL 450 mono-blocks (Main 2 channel) and venerable Anthem integrated One (Office 2 channel ). Not the new Paradigm stuff, the product I had was made by Sonic Frontiers.
I can parrot all the concerns expressed here.
Nonetheless, If one wants to take the plunge for what many consider their sonic benefit, here is my list of caveats, derived from owning such pieces.
(Echoing others) One, it is expensive to get into. Even the most entry level integrated gear starts at nearly $2K. You can buy one hell of an AV receiver or SS integrated for half or I dare say quarter of that cost. In the two channel realm there are a lot of outstanding integrateds that can be had for a little over $500.00.
Two, look out for the weasel pieces touting themselves as a tube design but are in fact hybrids. Tubes may be in the signal path from the preamp section, but usually they do next to nothing, and are for all intents and purposes are only there for looks. These are nothing more than a SS design with jacked up prices. I consider some of these pieces to be an rip off.
Three, be prepared to always be forking out considerable sums for their upkeep. This is the most painful part of owning tube gear that the sales folk do not warn you of. Average tube life is about 3 years. If you run your system more than 4 hours a day like I do. Their service life can be cut nearly in half. To get an idea how expensive this gets. The pair of MB 450 that I owned. Uses 16 power output tubes.Total minimum cost for stock Sovtek 6550we $34.95 ea., total cost to replace an set for this pair of mono-blocks was $559.20. It costs even more, if you do not want to stick with the factory tube and roll up to an KT88. Needless to say I no longer own the MB 450.
Four, Biasing is an pain in the ass. With heavy use it has to be done every 3 months at a minimum. 6 months on average. I would recommend designs that auto-bias. VTL, Balanced Audio Technology are a couple of manufactures that come to mind. The other option is to go with an design that uses an tube like the EL84, that can self correct for changes in grid voltages. My little Anthem Integrated used them for that very reason. It did not even have pots to set the bias with.
Five, stick with notable brands and dealers that will provide support for their product. A lot of the budget tube gear from China have had a number of quality issues. If anyone wants to get into them, I cannot stress enough the need to deal with manufactures that will take care of you after the sale. One of the issues, is sometimes when a tube blows, they often take out resistors and protection fuses that are designed to fail in order to protect the component's other parts from frying. If something trips, you want to be able to take it to someone and get it fixed.
(Echoing again) Six, IMHO, well engineered tube gear sounds like SS. Well engineered SS amps sound a lot like tubes. When I went to audition equipment I listened to a number of things. It was an toss up between, Audio Research, McIntosh, VTL, and BAT. I auditioned an BAT SS amp prior to the MB-450. The first thing my audio-buddy said of the MB-450 (Tube) was it sounded like the BAT (Solid State).
That for me sums up the Tube versus SS debate .