Hi Mark,
great question and I hope it's not too late for me to share my perspective on this.
Here's how I would evaluate this:
First, I would eliminate Zoho Creator and MS Power Apps. Why? For two reasons: first, these two tools primarily make sense if you're an existing Microsoft Office or Zoho CRM user. They are primarily designed as extensions to the existing MS & Zoho product suite. Secondly, both rely on proprietary languages: MS Power Apps uses a language called Power FX, which is unique to Power Apps. Zoho Creator uses a proprietary language called Deluge. This means that you will not be able to extend these applications in standard JavaScript.
Next, I would eliminate Outsystems. Why? It's an enterprise tool and starts at 1,500 USD per month. I assume you're budget won't support an enterprise platform, unless your client is a multi-national company.
Next, I'd ask where does my data reside? It sounds like you need to build a new database from scratch so that your end-users can perform read/write operations on it. Retool is primarily a front-end builder on top of an existing data source, so I'd eliminate Retool as well.
Now, coming to my recommendation: Five (https://five.co). Why?
- Five lets you create self-contained web apps.
- You're building on top of a standard MySQL database.
- You can extend Five through custom UI components in standard JS.
- Five deploys onto AWS, so industry-standard cloud infrastructure.
Coming to your other considerations: ease of maintenance and ease of use. There's a learning curve in any new dev tool. Ease of use really depends on your skills. Are you familiar with relational databases? Then building your DB will come easy to you. Are you familiar with JS? Again, then writing custom components will be relatively easy. For all of the tools you've listed, PowerApps is actually the most "beginner-friendly" tool, but given your background in development, I reckon you'd also feel quite comfortable in more dev-focused low-code tools.
Full disclosure: I work for Five, but the use case you're describing is pretty much exactly what we're trying to solve with our low-code IDE.