The most important thing about encrypting SSDs is to never write unencrypted data to them. The first problem with TRIM is that if you add unencrypted data to the SSD then attempt to encrypt that data in place, the TRIM function will most likely shift the unencrypted data to reserved space instead of overwriting it. This is the leak of unencrypted data you have read about. If you start off encrypting a brand new SSD then any shifting of old data does not matter because everything is encrypted. You can hope that the controller overwrites the shifted data with zeros but how would you know for sure?
The second concern about revealing a hidden volume is possible but not a certainty. If you make many changes to either the primary or hidden partition without making some to the other, it would be possible to examine the reserved SSD sectors and reconstruct a history of changes that could reveal the boundary between the primary and hidden partition.
If the SSD is going to be examined by a three letter agency, you would worry if you have a hidden partition with compromising data. For any other adversary, you would need to gage whether they would have the tools and time to do a full forensic analysis of the SSD. Then, it would only be a probability of the existence of a hidden partition. Again, you would need to determine what sort of pain your adversary would be willing to inflict to get you to reveal the password.