The item you have found should be OK. If you do a web search for the part number you will probably find a downloadable spec sheet for it (Maplins might have one hidden on their site). Manufacturers somehow manage to print about 20 pages about something the size of a geen sheild stamp, but in amongst the dross is usually an application diagram.
The notes for the one you found claim a max input voltage of 35, and a max output current of 2 maps. Treat this with caution - if you want 2 amps while losing 30 volts, thats a lot of watts to dissipate, and wouldneed water cooling.
Personally I would just go for a very ordinary 7805 regulator, capable of 1 amp, but if the supply voltage is ever going to be less than 7 volts the regulator will not behave. Then you need a "low drop out" version. If the supply is off a 6 volt SLA then you dont need a BEC, as modek electronics was designed to run off this type of supply.