WWAAAAYYYYY back, we installed our outdoor heat pump units on plastic pads that looked like concrete. Was on south side of the house so lots of UV. They started to degrade at about year 20ish - but only in a matter of a little flaking. They are still under the units today - 28 years later. Structurally all good.

He's recommending those because they are easier for him. What does that tell you?

Easier also can mean cheaper. My attitude with this kind of stuff is that I'm concerned with quality, function and suitability for me and my needs. An alternative that will function as I wish and have enough durability to be problem-free for as long as I may own a house, that's less expensive, is perfectly fine. I don't need to pay for having a "forever" standard.

To clarify: my landscape and stone contractor is going to provide and prepare the pads. The HVAC installer suggested the alternative. Fortunately, we're not quite yet in a jurisdiction that requires secured steel cages and padlocks to deter theft.

(I brought copper cable for recycling that had been left by the temporary electrical installation utility co.--an easy $659. )

A plastic pad has advantage of easily re-leveling in the future. Two or three condensers, a concrete/impervious surface pad may be cleaner, more sensible with that area of the house with their disconnects and linesets, and provide opportunity for design detailing (single pad, finish, matching adjacent sidewalk, next to concrete window well, etc). Or going to wall brackets if you have the height.

I have a plastic one filled with foam. One corner broke off so now that corner is sitting on a brick.

"The HVAC installer suggested the alternative."

The HVAC installer must be a very good installer, for it appears their talents in continuity of design and aesthetics are lacking. Most people's talents and gifts are not equally distributed across the entire field.

I take it that's a "no" on the aesthetics of simulated concrete.

In most cases nobody will see it or care; but it will be there to haunt overly particular Houzzers.