He'd be a great asset for the Scarlets. A steadying presence at full back or on the wing would balance well alongside the attacking flare of Steff Evans and NcNicoll, and it means that they don't have o rush a youngster like Cornbier onto the wing to replace Williams/DTH. If they want to challenge for the Pto12 again, and challenge for Europe, then proven quality is needed alongside raw talent, Halfpenny's quality is without question Imo. Can't be a bad thing either to have one of the world's best place kickers in your ranks.
I think it'll also be a great move for 1/2p, even if it's likely for a lot less than Toulon apparently verbally offered him originally. Under Pivac and Jones I'd expect to see Halfpenny's attacking game return, which should help him retain his Welsh starting berth. With Liam 1st choice for the Lions and so much attacking quality available to Gats out wide, Halfpenny's place is up for debate, so he'll need to improve offensively going forwards, no better place in Europe than at Scarlets.