How to validate–and kill–an idea quickly

Here's how I tried to validate–and decided to kill–a business idea quickly. We all have tons of ideas, but most are parked somewhere in our mind "for later." Don't do that. Look for a quick validation instead, then grow it or focus on the next one.

Problem
Starting my activity as angel investor, I find it suboptimal to use spreadsheets to keep track of investments and all other info about a company and a deal, and to have good analytics. Spreadsheets are ok, but not great for this purpose. And I couldn't find tools for angel investors (some tools are great for VCs and funds, but not for angels; AngelList is ok only for in-platform investments imho).

Idea
A business tool made on purpose for business angels: Keep the list of investments and any related info readily available, evolution of the portfolio over time, and analytics to monitor number of investments, amount, and ROI.

MVP
I build it on Bubble.io, powerful no-code platform. Steep learning curve to start, but it's crazy how with zero lines of code and $30 I managed to set up and run a web app on my own. Side project, 10-15 hours per week mostly evenings. Moreover, I love to learn. And building your own tool is so rewarding!

Validation
I talked about it and showed to other angel investors. Moreover, I reached out to great investors out of my network to remove bias.
The reaction was: "It's nice but..."

1. not a big pain–they make only few investments per year
2. spreadsheets & excel are not optimal, but they wouldn't use (and pay) a tool ad hoc only for this
3. investments are confidential info, they would be skeptical to use a startup for this
4. the real value added would be on updating the info automatically (company valuation), instead of tracking easy numbers and analytics
   A few feedback were positive, but from people who are not angel investors. So it's a confirmation that there is no use case for this, as it stands.

Decision
Kill the idea to focus on the other projects.

Reasoning
While there is space for such a tool, it would need much more exploration and development in a direction that goes well beyond angel investors, probably integrating functions for startups and competing with cap table management solutions and investment platforms. I like this space, but I think I have other more appealing and promising projects.

Post mortem on the process:
Maybe I could have saved time on the MVP. But beside being fun to build it, for a tool like this I think you can receive much better feedback from a MVP than just from talking. And it didn't take too long.

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Would you have done something differently? I'd love to hear that!