Remote desktop can put Sage 50 on a laptop. It does not turn Sage 50 into a field-sales application. The screens, the permissions, the need for a live connection, and the temptation to wander around the wider accounts system are all the wrong shape for a customer visit.
A dedicated mobile sales app gives the representative only what the visit requires: the customer, the price, the stock, the history and the order. It works offline. It is faster to use with a customer standing there. And it sends the result into Sage instead of asking someone to re-key it later.