Hi Skip,
My feeling is that if you are going to go metal, then it's more cost effective to just buy the tank with the metal upgrades to begin with. If you go with metal tracks, you will want at least metal drive/idler wheels, and that extra weight will almost certainly require gearboxes with metal gears.
Especially with shipping, it's probably not a good deal money-wise to upgrade after the fact.
The only reason I've done it is to make the purchases over time at lower cost along and along. In other words you can get the wife to buy into a $80 tank now, $50 gearbox next month, $100 tracks the month after that, etc. etc.
Do the tanks use 3 or 4 channel radio control units? I have a friend that has some used airplane controls and boards that he does not use anymore. Are these compatible with the tanks?
I'm not sure. I think aircraft use different frequencies than ground stuff. But I don't know how things pan out with today's 2.4 GHz stuff.
But basically you can control backwards/forwards movement, super-spin turn, gradual turn, barrel elevation (it just cycles, no independent up/down), turret turn left/right (but not in a complete circle), gun fires, machine gun fires. On 2.4GHz system units you can turn the smoke on and off from the transmitter and adjust the volume from the transmitter.
The linked Tiger on Ebay looks like shiny plastic and very much like a toy. Is this to be expected from the HL tanks? I have no problem repainting them and adding details; I just want to be comfortable with the purchase.
The pictures on Ebay don't always do them justice; the Jagdpanther often looks lime green in the photos! I own a Heng Long Panzer III (grey), a HL Sherman, and two HL Jagdpanthers. I find the finish very good on all of them, though I repainted one of my Jagdpanthers because it came with metal wheels and tracks and they are bright metal unfinished.
The decals that come with the HL tanks are not always historically correct and they have a shiny finish to them, so if that bothers you you at least would want to hit them with some dull coat.
Here you can see my two Jagdpanthers. The one in the foreground is stock with stock decals, the one in the background is my own paint job with photo-etched vent covers and aftermarket decals:
Personally I think Crius' link for the $90 Tiger with 2.4 GHz with smoke and sound is a great deal for getting started.
I really like the saggy look of the metal tracks and even the sound is different. But it's basically another $100 and it means you have to some painting to make the drive/idler wheels match. You'll probably want to paint the tracks, too though they dirty up pretty quickly.
Also take everything I say with a grain of salt. I'm new at this. Do whatever Crius says.
Steve