I totally understand your concerns about buying and merging accounts. In general, it’s always risky to merge a purchased account with your personal one. DE (Digital Extremes) has a pretty strict policy when it comes to compromised or bought accounts, and they do act quickly when they detect something suspicious, which could lead to a ban or even a permanent loss of your account.
While the temptation to get an Excalibur Prime is real, buying accounts can often lead to more problems than it’s worth, especially if they were obtained through questionable means. If you merge such an account with your personal one, there's a chance that it could trigger flags on DE's end, leading to penalties. It’s always safest to play by the rules, even if it means missing out on certain things temporarily.
In the end, it might be best to either earn the Excalibur Prime through legitimate means or wait for any potential promotions or events that offer it. I know it’s a bit of a grind, but it’s much safer in the long run. Just my two cents!