Can't see no reason why either the Hisense Roku or new TCL Roku (Currys) will have the full NOW Boost Feature because they both run on the Roku OS.
I did ask NOW to include these models on their Help articles to reflect this information but so far they haven't added them on the list.
Hopefully a Hisense Roku or TCL Roku ( Currys models) will confirm the above.
If you don't get a reply from either a Hisense Roku / TCL UK Roku owner on the Community Forum with the Boost Membership, then ask the question directly to NOW using the email address on this screen shot below.
My gut feeling is that both Hisense Roku and TCL Roku (Currys) does offer full NOW Boost features.
Maybe check out the HotUKDeals website and type Hisense Roku television in their search box, where there are a few different deals posted, where hopefully somebody has confirmed NOW Boost is supported.
Couldn't find the new TCL Roku Currys exclusive under the HotUKDeals search engine for any posts.
I have a sneaky feeling both televisions are Boost supported on the inbuilt NOW App.
To be on the safe side, get the answer directly from NOW using the email address that i posted.