Microsoft’s official policy states: "Using volume licensing keys for personal use is a violation of the license agreement." Technically, Ask4PC buyers are in a legal gray zone. You are unlikely to be fined, but Microsoft can disable your key remotely.
While the site itself may look cleaner than others, downloading Microsoft Office from Ask4PC is inherently risky: Malware Risks ask4pc microsoft office
(e.g., 15 out of 61 engines flagging it). While Ask4pc claims these are "false positives" due to the nature of patching, running such files requires significant trust in the source. Malware Risk: ask4pc microsoft office