I'm a newbie to this hobby & my first tank is a HL Challenger 2 (7.0). I have made a number of modifications but time will tell if they turn out to be upgrades!

My buddies have purchased metal tracks but I'm thinking they are an aesthetic rather than performance upgrade - any thoughts on this?

Cheers

There are many people here with way more experience than me (to correct me if I’m wrong) but I believe if you upgrade to metal tracks you have to upgrade the idlers and sprockets as well..for durability?!?

Just a thought/guess!

Mitch is correct.
The heavier you make the tank, the more you will need to beef up the driveline.

Plastic Hull, plastic tracks & plastic running gear = lightest configuration. Even Plastic gearboxes will hold up for years.
Upgraded with metal Sprocket/idlers = No issues, but plastic tracks may wear a bit quicker where sprockets engage (harder and possibly sharper edges).
Metal tracks with metal sprocket & Idler.= Mass increase due to the tracks. Usually 1kg or more depending on the tank (Short hull & narrow tracks are lighter.) Roadwheels can stay plastic. Steel Gearboxes will help immensly as the track mass is much heavier.

So up until this point, roadwheels and suspension arms are plastic. No bearings, just friction wear that is wholly dependent on the hull/turret mass. So tanks will run fine for years on plastic roadwheels without any bushing/bearings.

Metal Hulls = Mass. Steel gearbox is basically required. Metal suspension arms and bearings in roadwheels is usually standard as well. It is not often that you will see a factory metal hull with plastic running gear.

Examples: 
Heng Long King Tiger, all plastic driveline with 5000MaH battery masses about 2.5-3.0kg
Taigen King Tiger, all metal lower hull, metal turret, and metal driveline w/ same battery masses 7-8kg.

Great info - thanks. So am I right in thinking that metal tracks look good but don't do anything in terms of improving the tanks performance?

Yes and no... Mass can give you better traction. Which can equate to more stresses, but also better performance. Traction = ability to climb hills.

All depends on the track design too.

Metal tracks do look GD awesome though.... Track sag on a KV-1 is superb!

Once again. The massive repository of Jarlaths knowledge is opened. Ha haa
Yes. The KV's and the IS's look great with a good sag!

The upgraded tracks on Martin’s KTs and Ren’s JT look incredible with a healthy amount of sag.

My buddy has a Chall 2 with metal tracks but otherwise identical to mine so we will compare performance (once we have other mods completed). I agree that the metal tracks look great but on the Chall they are hidden by side skirts.

The metal tracks look great but just my opinion for battling Tamiya tracks are the best except the KT ones. The sag I ran around with on my Tamiya KV-2 was pretty insane and they stayed on. No pins coming out. Look at Victor's KT. No other KT can battle with his light plastic tracked HL so I would say plastic tracks is the way to go for battling. Problem is that Tamiya tracks cost as much if not more than most Taigen/Mato/HL metal tracks