AHK is definitely great, Nora. I don't try to dismiss it. For straightforward text expansion one doesn't need to look further; and you can't beat the price either.

However, I think that a more powerful tool could come in handy even in relatively simple use cases. From my experience, relying on mnemonics alone is somewhat limiting. From a certain number of phrases (which, I admit, changes between people) it could even become counter-productive as most people will resort to using only handful of common/memorable phrases.
Also, the simple AHK script lacks some powerful functions, such as inserting dates, date calculations, inserting the clipboard content, and so on. They could be baked into it, no doubt, but it takes some doing (or maybe there is more advanced AHK scripts available out there already. I haven't looked into it).
It's could also a little bit of hassle when having to frequently add or manage phrases. There are ways to logically separate different categories of phrases, which is something I recommend in general, but to me it's still not ideal
Maybe I'll write a blog post about how I categorize different types of phrase using prefixes to prevent, well... minimize, accidental expansions and replacements.

I also like to use the text expansion tool as a system-wide auto-correct library for common typos or for different writing styles (contractions and abbreviations vs. no contractions and abbreviations) and I find it easier to manage all of this on a more powerful tool than AHK. The integrated Clipboard manager is also very convenient and in most cases saves running another tool.

I believe the feature in PhraseExpress Professional that clashed with Studio's Autosuggest is Autocomplete. The function that analyzes everything one types and then offers suggestions to save typing. Personally, I have found it annoying and distracting. If Autocomplete remains on when one translates, it becomes cluttered with irrelevant suggestions when working outside the project, as well as with entries that are relevant outside the project but are pointless withing the project. I suggest turning it off unless v13 added the ability to limit it only to certain programs (haven't checked). I also consider that system-wide Autocomplete a privacy concern. AutoSuggest works much better for text predictions within a project, but other than that, I haven't experienced any conflict between PE and Studio.

I wrote to Jan (the developer of AceText). Hopefully he would consider at least implementing hotkeys assignment and input fields. That would probably make AceText my first recommendation as a tool that covers most bases and bridges the gap between a simple AHK script and more powerful, but expensive, tools such as PhraseExpress that have some features translators don't really need.