What is the threshold to prefer polyphase channelizer over FIR filtering? A wideband signal need to be processed to extract several narrowband channels from it. There are two straightforward approaches to do so:


For each narrowband channel shift frequency and filter it with FIR filter.
Implement polyphase channelizer and select only those chunks that correspond with target narrowband channels.


Considering the following extreme situations:


Need to select 1 narrowband (25 kHz) channel from a wideband channel (56 MHz)
Need to select 2048 narrowband (25 kHz) channels from a wideband channel (56MHz)


It seems to be obvious that in the first case time-domain filtration is more efficient and polyphase channelizer is more efficient in the second case.

The question is what will be more be more efficient (require fewer FPGA resources) if only 12 (25 kHz) arbitrary placed channels need to be extracted from a 56 MHz wideband signal?
A polyphase channelizer is not a special kind of filter. It is a structure that works well when using filters in multi rate settings. Polyphase is a sampling rate conversion method that leads to efficient implementations that are useful for building filter banks. The efficiency comes from only having to design one filter. The downside is that the extracted channels have to be uniformly allocated and the signal sample rate has to be an integer multiple of the channel's bandwidth.
Use a channelizer for 2 more channels that are uniformly allocated.