Old school thinking. If you want protein, buy protein and not a "weight gainer".
The bulk 5-10lbrs will do the job if looking to boatload grams. If looking for something a bit more functional/effective, consider a good cold processed whey that includes di-tri peptides. This type of whey is research proven to boost glutathione, boost immunity and improve nitrogen retention above and beyond heat treat whey/other proteins.
If cost is an issue (and it is for most), reserve use for peri-workout.