Difference between Siemens 6ES and 6AG ?

I don't have a lot of Siemens experience so I'm posing some simple product selection questions.

My client is proposing an S7-1500 system that uses the ET200SP hardware platform, starting with a small CPU 1510SP-1 with a single ProfiNet port.

The distributed I/O will also be the ET200SP platform, so it needs a ProfiNet adapter.

The one he called out is an IM151-6PN network adapter, part number 6ES7155-6AU00-0CN0.

The Siemens website says that part number is out of production and the recommended replacement is part number is 6AG1155-6AU01-7BN0.

That's where I get confused. That new part number seems to be a high-performance or high-speed or "SIPLUS" product, rather than an ordinary ET200SP network adapter equivalent to the IM151-6PN. I don't know the difference between 6ES and 6AG classes of Siemens products, so if anyone can compare them to A-B families of products that would help me to understand.

They're trying to get commonality of parts with a S7-1500H redundant system on the same site (mine is not redundant), so I'm thinking maybe they need a specific part or a high-functionality part.

What's the most common adapter for ordinary ET200SP digital I/O modules ?

I'm more interested in a module that the customer will be able to get in Florida for 10 years, rather than one that's cheaper or smaller.

My successor part comes up as follows, not a 6AG.... number.

I would use a stand alone CPU (e.g CPU 1511-1 PN) and use distributed I/O from that.

My understanding of the difference between 6ES and 6AG is that the AG is the extreme conditions version. They can withstand more vibration, different temperature ranges and are conformal coated.

Last project I did, I used all AG hardware but in TIA Portal I used the ES number in the hardware configuration.

Hope this helps