Is that too shallow?

Too shallow for what?

Measure your own sinks to help you decide.

many of them don't have any back panel

Not needed as the vanity will be fastened to the wall.

In my first house I had deep bathroom sinks -- cheap sinks you'd see at Lowes. I didn't realize what a luxury they were. I could bathe a baby in those sinks, wash out a blouse. I miss them.

In my larger, supposedly nicer house, I have shallow sinks. Really pretty 1970s sinks shaped like sea shells. If I turn on the water full strength, they splash back at me. More expensive isn't nicer.

Also, duplicate sinks in a 5' vanity leaves you with no counterspace and no drawers. A single sink is superior.

Yeah, splashing is what I'm wondering about. Our current sinks are 6 inches deep. My husband already gets water all over the place, though I don't. So I do worry about how much worse 4 or 4.5 inches might be.

We currently have a 5' vanity with 2 sinks and it's fine space-wise. I'm not sure why so many people think it's not big enough--i see a lot of people saying this. Maybe we just don't have a lot of stuff. My husband and I regularly use the sinks at the same time before bed. 5' vanities do have drawers, though ours doesn't. On our countertop, we have soap, toothbrushes, toothpaste, floss, his razor and that's about it. We don't use hair dryers or even brushes (curly hair--just comb in the shower). My hair gel lives in the medicine cabinet along with deodorant and face creams.

Some of the sinks I'm seeing look like they have flat bottoms, which might be good for bathing a baby but seems like there would be water sitting all the time. I hate that I probably have to choose something without seeing it in person. I know I want an integrated sink, not undermount.

SSome

I feel like those sinks would be too shallow = water splashing. My SO already splashes water around and his sink is a couple inches deeper than 4 - 4.5".

It would cost me less money to have a 6' countertop made + installed out of my fabricator's most expensive quartzite material (which could include a thicker mitered edge if needed to house more of the depth of the under-mounted sinks) for less money than the cost of that prefab countertop with sinks. He also has different options for pretty inexpensive (but still nice) vanity sinks. I am purchased Kohler sinks for my vanity - I didn't know that he offered sinks + I like the look of mine so I'm happy.

He made my countertop with a thicker mitered edge in order to not lose any of the space in the top drawers (my vanity is all drawers - 83" wide). It was only about $400 more than the cost of that 60" prefab countertop with sinks (and I selected expensive material for my countertop).

You could find many options in a fabricator's graveyard (where they keep pieces of slabs that weren't used to make countertops). There will be a variety of different types (quartz/marble/granite/quartzite/porcelain) - at a 60" width, it's likely that you'll find something that you like.

Have you looked at vanities in a kitchen store? Cabinet lines usually vanities and may run you less than what you are seeing.