After signing in to my Vanguard account, there is a front page saying that I could convert my mutual funds into ETFs tax free. Would it be worth it?
If the underlying reference is the same it shouldn't really make any difference. When you buy or sell a mutual fund you trade at an unknown price (end-of-day price) while if you buy and sell ETFs you have more control at which price a trade gets executed, this might be better or worse than the end-of-day and in the long run will be the same on average.
The big pro for mutual funds is that they discourage trading. If you have a slight urge to try and buy, sell, time and be smart about it, mutual funds are likely to be a better option as the former strategy is highly unlikely to give equally good results to just buy and hold.
ETF might or might not have a lower minimum amount (you can buy just 1 share), mutual funds might have a higher minimum amount. This might or might not be relevant for you. Mutual funds are also better suited to repeating orders such as "buy this fund for 1000 dollars on the 10th or each month" or whatever.
As long as you just buy and hold they will be very, very similar as long as the unerlying index is the same.