what do you mean? all current wd ssds use nand. what's the other one that doesn't use nand?

if possible, don't save the extra few bucks, and get 850 evo. you get 2 more years of warranty.
if you're looking for entry-level ssds, i suggest you look at mainstream options, because of the following reasons:
1. the price gap between mainstream and entry-level is too small;
2. the performance gap between the two is relatively significant.

if you're really having budget constraints, well, entry-level is still fine for light usage, and they're still ok compared to hdd, when the usage is within their limits.

I strongly urge you two to get the Samsung 850 EVO
Their firmware updates is frequent & RMA services is top of the line

No doubt the price is higher but think of the 5 year warranty rather than other brands that only provides you 2 ~ 3 year warranty

you could consider 860 evo while you're at it. it's supposedly the successor of the 850 evo

860evo is like 23% more expensive than 850evo. yes internally 860evo has new 3d-nand, there is no significant performance gain.

nice; yes it will be fine when you're using it within its limit (light client usage)