The Mete is a step up on the current SFX. Strangely, it is priced at $430 if you look around which seems to be below the current non mete sfx. They made some significant changes to the bulk of the grip on the mete model. I bet dealers are trying to get out of the current SFx inventory as the Mete takes over. There is a SFx 2 coming at some point too. That has been known for over a year, but still nothing. It's possible the Rival will become it without the Walther copied Dynamic trigger. Who knows.
The Rival has a 5" barrel to meet some gun game requirements where the SFx is too long. It is at $630. It has the new grip as the the mete, both are improved from the current sfx.
If you are stuck on the TP9DA, the true comparison is with the Walther P99AS. It doesn't look like we've had a shipment of those for over a year though. The P99AS is significantly smaller all around vs the TP9DA in feel. It will feel significantly more so in your hand. However, is that worth the cost different to you and can you get the P99AS anymore. If not, there is no other SA/DA decocking striker like it.
If you can stand not to have the Walther copied Dynamic trigger in the Rival and can tolerate the Mete .25" longer barrel...man, the mete SFx at $430 is one of the better current deals out there.
Again, Canik copied the Walther sear house. The current PDP is about $550