Originally posted by VoiceOfReason The only advantage with that combo is weight. That is it. The DFA 150-450 is pixel peeping sharp even wide open on the K3 and K1. Even adding the 1.4tc still allows pixel peeping when pared with it, and gives up to 630mm f/8 that is very, very usable and nice and sharp too. Moon shots with that combo are awesome. Birds are good too.
That's helpful VOR because you have used both. And since the OP in this case is happy with the Bigma, weight might not be a big issue. But I pointed out the alternative because many people going to a longer telephoto option for the first time will find carrying and using a 2kg lens a challenge.
For completeness, we should add that the DA*300 + TC costs about $1100 + $500 whereas the DFA 150-450 costs about $2200 and the Bigma $1660 (using B&H prices in $US as a comparison). Even with the over-priced TC, the prime is the cheapest option.