To properly test a business idea, practically every start-up book recommends setting up a landing page, funnelling traffic to it and testing whether the idea (main value proposition) will gain traction, measured by number of subscriptions.
The main problem that I have with this approach is that unless you're selling a very simple product/ solution, a simple and cheap landing page won't cut it. You will have to spend substantial time and money on a landing page that will be good enough to make a proper impression with the target customers. Why? Target customers care about the design of the page (it's a marker of trust) and user friendliness (even for SaaS) of the site/ app/ product etc. (it often not about an idea but about its execution - think smartphones and mp3 players). Unless the landing page will be able to deliver all that you won't be able to test the idea properly (the idea might be great but an improper landing page will fail to confirm it).
Have you thought about skipping the landing page and going straight to producing an MVP?
If you're a bootstrapper you are probably not creating a very expensive SaaS or a product (you're not in biotech, finance, energy, space and similar sectors). With a little bit of ingenuity you can probably create a simple MVP for a not much higher price than a landing page. Testing your idea with an MVP will not only be a much better predictor if you're on a right track. You'll also have more fun doing it (don't disregard the role of enthusiasm in your life - it's impact on happiness!).
So, I'd say landing pages have their place either when you're developing a very simple product/ solution that you can properly present on the website or when you're creating a very expensive product, where even the cost of an MVP is substantial (or at least substantially higher than a landing page).