Clear to Fire says,
RN-you will be expected to be a naval officer first and an ATCO second. Expect lots of sea time initially with more land posts coming as you progress in your career
but, assuming he's talking about Officer entry he's a bit off mark there.
A naval ATCO may do a litytle time at sea during basic training, but after Dartmouth, will go to Joint ATC School at RAF Shawbury. Then move to an airfield. More training, then complete a tour (about 2yrs). 2nd tour may or may not be at sea (there aren't that many sea going jobs around?) In a typical officers career they may get two, three if you volunteer, sea jobs max... (You might expect to get short detachments to sea to cover exercises etc, but these will typically be no more than 1 month at a time). Things may change idc when the new Carriers come into service, but for now the sea/shore ratio for ATC is good.
Rating ATC entry (via the AC branch) is different. Most AC work is afloat so they will get quite a bit of time in up to and including PO (and they love it)