How to estimate a competitor's ballpark income?

I imagine this is a very tricky question but hopefully I can get a few insights here.

I am currently wrapping up a personal project (SaaS) that is aimed at a fairly new niche market. There is a competitor, although I would argue not direct as we have different approaches to the problem. I am about to approach potential investors and I want to lay down for them some ballpark figures of how much revenue the competitor is generating.

So far the best I can do is to get a traffic estimate of their site, and apply to this number some average (but I am afraid quite irrelevant) conversion rate. Let's say they have 100K visitors a month (on commercial site, not app itself), then I could say that 5% get a free trial and 10% of free trials convert. Is there anyway to get anything more solid than this?

As a former consultant, my advice is to say: try 3-4 different estimation methods which should give you a range of numbers:

1. Do a traffic estimate, and estimate conversion ratios, as you suggest.
2. Try to figure out their number of employees (website, even calls to their help desk), and whether they are making huge profits, breaking even or losing money. This gives you a good estimate of their costs from which you can approximate their revenues.
3. Do a literature search for any news on their company: sometimes you can see, e.g., a financing or other news.
4. Talk to their customers (who will presumably become your customers too), and find out everything you can about them.