Apart from the jurisdiction, I don't see any reason to invest in...

Apart from the jurisdiction, I don't see any reason to invest in ARR.

Data :

Grade

LIN is ~2.5% / 25000ppm
ARE is ~0.33% / 3300ppm

This is by far the most important factor in this comparison. Grade is almost 8 times higher for LIN.
The reason this is important is because of the CAPEX and OPEX difference in the feasibility studies down the track.

To produce the same amount of saleable Rare Earth Concentrate, where LIN would need a 1mtpa concentrator and associated infrastructures worth maybe 200-300m$, ARR would need a 8mtpa more likely to be ~1-1.5bn$ with higher opex cost as well, higher energy costs, labor costs, bigger mining fleet etc...

There's a reason people say grade is king.

That saying is especially true for small caps considering how difficult it is for them to finance projects with high Capex.

TREO Contained

LIN is ~5mt for 200mt @ 2.5% TREO
ARE is 4.73mt for 1.43bnt @ 0.33% TREO

We can say it's likely to be equal on that front considering both have enough rare earth to be tier 1 and plenty of exploration upside.

NDPR Ratio

LIN is 21%
ARR is 24%

Not much to say, pretty similar, slight advantage ARR on that front.

Radioactivity

LIN is averaging 40ppm Thorium / 7ppm Uranium
ARR is averaging 60ppm Thorium / 7ppm Uranium

This looks pretty similar at first sight. Except it's not at all. The reason why is linked to the grade.
To produce concentrate, you push ore through the concentrator plant and, during this process, you separate the monazite from the rest of the ore through magnetics or gravity for example. Radioactivity is in the monazite so you concentrate it as well.

This means that to produce 1 ton of 60% TREO concentrate, LIN's ore will have to be concentrated 24 times. (60%/2.5% = 24)
Final radioactivity in the concentrate will then be :
- 960 ppm Thorium
- 168 ppm Uranium

Now for ARR, to produce 1 ton of the same 60% TREO concentrate, you need to concentrate it a whopping 182 times !!! (60%/0.33% = 182)
Final radioactivity in the concentrate will then be :
- 10920 ppm Thorium
- 1284 ppm Uranium

So there's a factor 10 between the radioactivity of the saleable concentrate eventually produced by the two companies.

For another comparison, Lynas at Mount Weld has a 5.4% headgrade, 750ppm thorium and 30ppm Uranium in the ore.
This means that it needs to concentrate it 11 times to reach a 60% concentrate to give 8250ppm Thorium and 330ppm Uranium in concentrate.

So LIN will produce a concentrate close to 8 times less radioactive than Lynas.
On the contrary, ARR's product will be even more radioactive than Lynas, with much higher uranium and higher thorium.

Surface/Environmental Footprint :

This one is definitely advantage LIN.
Considering ARR will have to move 8 times the volume of LIN and that most of it's deposit is <150m depth, they'll have to dig a shallow open pit that will have to move year after year so they will impact a large surface area.

LIN being much higher grade and being continuous at depth means it will be a simple open pit with classic stopes most likely limited to a simple 1km square even long term.

Final personal word

Rare earths are not rare at all. There are already enough proved deposits in the world to last over a 100 years with the current ~200.000t per year NdPr demand (even though that's increasing fast).
This means that only the cheapest and easiest to extract/process orebodies will be successful.

Rare earths are not copper where there's a shortage of high grade deposits with a mature and stable global demand so mining giants develop high tonnage/low grade mines.
This will most likely happen in 30-50 years in the rare earth industry but it's to early to bet on large low grade deposits yet in my opinion.