It depends how much time you have to burn, and how much traffic you handle. If you have trivial scaling needs or want to spend 10x the human time managing that setup, then go ahead. You use something like opentsdb when you have hundreds of thousands or millions of ops per second and don't have the time or desire to deal with a database that you have to build your own partitioning + resharding + failover + recovery systems on top of.

B+ trees are not optimized for the kinds of write-heavy workloads that you typically stick in HBase (LSM-tree).