Welcome to FT!
In general the main risk is award availability disappearing between purchase and booking. Typically $2000 for one way is rather high; 600-1000 for F (even lie flat on DL, HA, or some UA) is more common so from that prospective buying miles is not the best value. If you dont have flexibility and your only choice is miles for 1K or paid 2K - buying miles is definitely a great deal; at the very worst they will become AS miles with lots of redemption options.