It is the Variant ID, not the model number, which determines the update schedule of a YouView box. A list of Variants can be seen on the YouView website at http://support.youview.com/articles/Self_Service_FAQ/Software-Update-1373538549510
Fifth character = 7 means the box is on the retail update schedule
Fifth character = 8 means the box is on the BT update schedule
Putting a box's serial number into the Warranty Registration form on the Humax Digital site should confirm the box's Variant ID. http://www.humaxdigital.com/uk/wregistrations.php
Can be useful to know if buying online, since sellers/retailers don't often include information on a box's updating destiny.
Whether 'tis better to be in the hands of YouView or BT for updates is a moot point. Retail users effectively get to debug each update before it's released to BT/Plusnet users.