Some liberals may blanche at the agency reporting it (as a conservative free market think tank) but the data goes back to 1995 and it is very interactive and informative and some underlying assumptions can be undermined by this such as the direction certain countries are heading in with regard to say labor freedom, government integrity, and other factors that people even those who openly disdain 'free markets' can get behind from a human rights perspective.
Example you can see that the US got surpassed by Canada in 2009 - likely due to US regulations following the economic crash. Or Canada's labor freedom dropping out of the top category in just the past two years.
I see no evidence though that these ratings correlate in any way to predicting which nations will have stronger future GDP. Given the measures, I have no doubt that these rankings correlate very strongly with which nations will have growing wealth inequality.
Anytime an organization uses a loaded term like 'freedom' except in that terms' original meaning/context that should tell you that the organization's work is for propaganda purposes and not for governance purposes.
GDP is a rather inaccurate barometer.
I prefer the Fraser Institute's Human Freedom Index which combines Personal Freedom with Economic Freedom. The one I mentioned was from 2017. Frankly, without ability to have freedom to change jobs, freedom to start a company, etc then one is in a position of depending on the whims of the locality and how its civil rights conditions are. For all the complaints of bias though if you actually look at the rankings you can see that economic freedom can be achieved while maintaining civil liberties and there is a correlation between the two as the Fraser one shows.
If that was all there was to it, that would be fine, but looking at the Heritage Foundation website it includes 'property rights' which generally means 'no regulations on developers', 'tax burden' which generally means 'low taxes on the rich' and 'labor freedom' which means 'no unions.'
I think it's pretty clear that what these rankings really favor are countries that have policies that lead to increasing economic inequality. Again, I haven't and I don't know if anybody has done a comparison of nations that receive high rankings from the Heritage Foundation or the Fraser Institute, but I would certainly expect a very high correlation not with increasing median wealth in those countries but with increasing income and economic inequality.
Of course, if your values are that the rich deserve to be rich and that the poor deserve to be poor, then you are perfectly welcome to take these rankings from the Fraser Institute and the Heritage Foundation seriously, but I think we should all understand what these rankings are most likely really measuring.