I don't know much about Merlin's accuracy with bird calls, yet unfortunately Seek isn't enough to accurately identify plants and often leads to incorrect or overly confident (ie wrong) identifications when not enough information is available. In keying out plants, especially at the level of distinguishing species, features needed for identification often can't be gleaned from a single or even sequence of phone photos. Blooms (not always present due to seasons), internal flower or fruit structures, seasonal foliage, and features at photo incompatible scales (hairs on a leaf and also overall branching structure are hard to capture in one picture) are all common diagnostics in keys, and using neural nets biased to suggest the most commonly occurring plants leads to similar yet less common ones being misidentified.
It's a great resource for getting down to the family or sometimes even genus level, yet botany knowledge and a local or regional key/flora is really needed beyond that in most cases, unfortunately. I still think it's great for folks who otherwise would never get into botany and also raising natural awareness, yet I do worry about its impact on citizen science by giving a false sense of confidence in shaky algorithmic classifications, potentially tainting data collected for more rigorous purposes.