I'm almost a beginner in the chess world who at the moment only plays online and watch various chess lectures on youtube.
I'm thinking about using http://www.elometer.net/ on a monthly basis in order to see my progress over time.
What are the pro and cons of doing that?
Elometer is just a test.
A true rating system score is only relative, i.e. it means something only among the members of a group (that should be big, but is finite). After choosing Elo, ree, TrueSkill, Glicko - here's a comparison - or what you like better, it makes no sense at all to compare your score within a group with your or someone else's scores in other groups, or do some other abstraction.
You can go on playing online and check your Elo variations, or record a subset of matches in another rating system (as aforementioned Glicko, TrueSkill or rankade, our free-to-use rating system), or in case use them for your club, or friends, and track your score vs matches or time. These are good ways to measure your progress.
Well, the main problem with these tests is that they aren't reliable. They can only give you a rough indication of your playing strength, nothing more. Maybe something accurate to 100 rating points, and it's very hard to gain 100 points in a month, even for a beginner. So it will be hard to measure your progress on that scale.
Also, taking the same test over and over again makes you recognize certain test questions, instead of solving them with pure chess skills. And lastly, they measure your ability to solve chess diagrams, instead of your playing strength. That encompasses many more things like an opening repertoire, knowing how to spend your time over the game, etc.
If you are playing online you should already have an online rating which should be enough to track your progress.
As far as I can see, the website you list tries to give an estimate based on how well you solve tactics puzzles. Tactics is important, but not all to estimate playing strength.
At least at some level other aspects like openings or strategy/developing long time plans will become relevant and it is difficult to assess these in a test.
Also note that ratings (e.g online and FIDE Elo) are not comparable as they always depend on the player pool. If you only want to track progress it is fine if you stick with one rating system. I don't see much need for another test.
answer: No cons. More info can only be better, but it is just a number to measure an abstract skill. The key is to not read into it anything other than that.
As mentioned already, you should be playing online as much as you can (G15 at least, blitz less, bullet never), and that will give you a good approximation of your rating.
But it is just a number, something you should not be married to.
