Payment on delivery means mobile, not portable
A device that leans on premises Wi-Fi is the wrong tool for a driver. Payment on delivery needs its own mobile connection, and whether that data is included or billed separately is worth establishing.
What happens to a transaction when signal drops mid-payment is the question to ask, because it will happen.
One terminal per vehicle adds up fast
Device costs multiply across a fleet in a way they never do for a single site. Ten terminals at a typical rental is a serious annual number, and it is the line most worth attacking.
Tap to pay on a phone is worth considering per vehicle, particularly where card payment is occasional rather than every drop.
Fleet cards and commercial mix
Business and fleet cards are common in this trade and cost more to accept. A rate quoted against a consumer card mix will not survive your actual traffic, so have it quoted against the real thing.