The tesla charger is not Cheap as you suggest.
Cheap is also a synonym for inexpensive, you know - that's how I was using it. You were the one who brought up the price of the Tesla mobile charger, presumably to highlight it as cheaper than the alternatives and as a factor in favor of the option you're recommending. That presumption is confirmed by your above post where you call it a bargain. $200
is cheap compared to the alternatives. But that is deceptive because you left out the largest cost - $300 for the TeslaTap, which is a required element of your solution.
I don't see your suggestion as particularly cost effective, while your suggestion seems to make the cost a prime factor. My post was intended to make that clear by spelling out the actual total cost.
The Tesla Mobile Connector is $230 on the Tesla website, can only charge at 32A, and requires a $300 adapter to use with a Rivian. The Rivian COMES WITH a mobile charger that does the same thing for free, without any adapter needed. And the Rivian charger can be used with the OP's Tesla because the Tesla includes a J1772 adapter. So the OP can save $530 and not buy anything, if a mobile charger solution is desired.
The Tesla J1772 Wall Connector is $550 on the Tesla website, and can charge at the full 48A available on the OP's circuit and does not need an additional $300 device. This will work with both a Rivian and a Tesla because Teslas come with a J1772 adapter. This is a more permanent, robust, and higher current solution for essentially the same price as what you suggest, and if the OP is going to spend money then a hardwired charger like this is probably a better choice.
If there is a need to charge two vehicles simultaneously, then perhaps something like the Wallbox would be a better option than either, since it can be hooked up in series with another Wallbox to do charge sharing for two vehicles on the same circuit. Wallbox is not the only charger with this feature - the Tesla Wall Connector can do this as well.
The Tesla tap adapter is a great piece of engineering and there is no "plastic" in this.
Literally the first search result for "delrin" is the sponsored link from DuPont, titled:
Delrin® Material By DuPont™ - DuPont™ Delrin® Plastic
So yes, it's plastic like I said, by definition and as described by the manufacturer and patent holder of that material. And again you seem to have missed the point. I guess it's my fault for being so terse, so let me add some words:
TeslaTap, whether good or not, is an extremely expensive solution for what it is. You can buy the entire Tesla Mobile Connector for only $230, which itself has quality "plastic" connectors at both ends, plus power electronics, lots of copper cable, a pretty housing, etc. Compared to $300 for the "tap" which IS almost entirely plastic, with some metal for conducting the current. Comparing the two, it's really hard to justify the $300 for the TeslaTap, no matter how good. The Lectron adapter is similar to the TeslaTap at half the cost, but even $150 is a bit hard to justify for something that is essentially and almost entirely a piece of plastic.
So no, the Tesla Mobile Connector is not the extremely great bargain you make it out to be. It is one solution, and it's not a bad solution, but it is most certainly not the cheapest solution and probably not the best solution for the OP unless there are other considerations that weren't mentioned.