Either EA7500 is a much better choice than the A7. The A7 is an old design with an old and, today, relatively slow, CPU. With 16MB flash and 128 MB memory, an A7 only has just enough memory. I would not spend/waste $60 for a "new" A7 well on its way to obsolete that I can pick up used for $20.
Either of an EA7500v1 (ipq8064 target - dual core 1.4 GHz armv7) or EA7500v2 (ramips MT7621 target dual core 880 MHz mips) is supported by OpenWrt. Both have 128MB flash and 256MB memory, which is pretty comfortable. I can't help you with deciphering which is which on amazon. Used on ebay, where you can hopefully see a picture of the label indicating V1 or V2, may be a better option to know what you are getting.
The EA7500v1 has the better/faster hardware if you want to run SQM faster than ~185 Mbps or are looking for something to support a fast VPN on the router.
If I was spending $60 on a "new" router today, I would look for an EA8500 used on ebay for ~$50. You would need to open the case to flash it the first time with a USB to serial dongle (which will cost you another ~$5-10), but its worth the effort in my opinion. Light years ahead of an A7
Even more interesting is that version 3 CPU is listed as "Dual-core 1.25 GHz". Either a typo, or it suggests that it is neither ipq8064 like v1 nor MT7621 like v2. Wonder what CPU/platform is used by v3.