Bar size is a liquidity choice as much as a budget choice. The gold is the same metal. The premium you pay, and how easily you can sell only part of a holding, are not.
What changes with size
Very small bars, such as 1g, 2.5g and 5g, are simple to gift or sell one at a time. They usually carry a higher price per gram because minting and dealing costs are spread over less metal.
A 10g or one-ounce bar (31.1 grams) is a common middle size in this shop. A 50g, 100g or 1kg bar puts more metal in one piece. The premium per gram is often lower. You cannot sell half a bar without cutting it, which is a different and worse object than the bar you bought.
Fineness and brand
Most investment bars we list are 999.9 fine gold from named refiners. The product page states the mint, the weight and the price. Dimensions are shown only when we actually have them. “Random year” or a specific year is stated on the product when it applies. Do not assume a year the listing does not give.