If not careful and patient, this could waste a lot of money. I’d suggest watching hundreds of performed whistle reviews on YouTube, and read reviews that go into detail about tone, playability, wind requirements, chiff, and what happens when you play that whistle model towards the very highest and lowest notes and what happens, or where the whistle starts to fail or change character, and just how bad as the note response starts to change. Reviews that demonstrate a range of keys in one model, often with multiple other whistle makers/models used as a helpful comparison, are very helpful.
One whistle design will often not sound the same through the full range of keys, from high E to low D or even lower. A MAJOR consideration in how a whistle sounds and plays, is many whistle makers will use one bore size for many keys, and that adds to the variety of responses and tones you get, instead of providing a uniform whistle response across all the keys. Live performance reviewers will often point that out. For instance, if one bore size is used for soprano E, D and C, or alto A, G and F, the playability and tone may vary considerably. If for example the alto G is the perfect match for playability and tonal range, between bore size, key and whistle response, then the F and A key whistles with that same bore size will respond differently. That affects wind requirements, it affects tonal character, it affects loudness, it affects octave jumping, intonation sometimes too.
So with all that, and more, in mind, I would clarify what you want in tone and playability for each range (soprano, alto, low) and expect to find different makers and different models that will satisfy you, and expect that one maker may not.
If you buy a whistle to try it out, or just try one out by borrowing it, play it enough to really understand what you’ve got, and be clear on what is acceptable and what else you’d prefer. Different whistles often require adjustments in the players applied level of air and control, so don’t be hasty. If you were given 25 different alto G whistle models on a table and given 5 minutes to try them out, you would not have time to really clarify how you like most of them, because you didn’t have time to give the tryout process enough experience. Same thing goes for trying out a range of keys using one model of whistle; you need time to find the subtle and not so subtle variations.
Another consideration is that whistle designs (by quality makers) vary over time as the designs and construction methods improve. So for example a key of C whistle that is one month old, and a key of F whistle from the same maker that is 20 years old, if given the same model name, may not really be the same design or respond the same way.