How about upgrading your clients' wifi at the same time? Get
any external dumb HDD and attach it to a USB port on an Asus RT-AC68U (or the
T-mobile branded equivalent thereof) running Tomato or DD-WRT. Roughly the same price as a WD My Cloud solution or similar, but your clients will get the added benefit of more stable and faster wifi -- a priceless benefit when streaming movies over the WLAN. You can also offer a premium service to tailor QoS for your clients, prioritizing VoIP / Skype for calls to grandma, games for low latency FPS, Netflix streaming, or whatever else the client values.