diskless boot only thing of interest here, i assume they will sell these rigs for more cost than their individual parts cost (so would be cheaper to buy and construct it yourself).
Though diskless boot only saves about 15$usd/rig given that's the cost of a 60gb ssd from china these days lol
and risking for 15$ per rig to have an entire farm to go down in case of server failure, if you really want to go cheap do it with USB

Not to mention that on the server side yo have to have at least 4+ SSD and good know how much RAM