Richard,
Let us know your thoughts when you receive the amp. I'm assuming you bought it new since you're concerned about burn in. If so, then there probably will be a break in period. However, the good news is there should be some kind of warranty on the tubes, usually around 90 days. This will give you plenty of time for burn in and to decide if you like it or not. It should also give you tube replacement for free should you need it the first 90 days.
The cheapest you'll find a spare set of tubes will be about $110.
Cheers,
John