This comes down to personal preference as both do the required job to a high standard when applied correctly. The massive benefit RubberGum boasts is its simplicity to use. This means that correct application is far easier to achieve and requires far less skill. Despite this, RubberGum is only tried and tested on horizontal joints. The weight of the item being sealed compresses on the RubberGum and creates a strong bond and waterproof seal. This can not be achieved to the same level on a vertical joint which is where silicone bounces back on the scoreboard. With an Insignia shower, RubberGum is supplied with the vast majority of the range so the choice is down to you, the customer/installer.
NOTE: Never let Rubbergum and Silicone touch each other. Due to the chemical reaction, it will turn Rubbergum into a chewing gum texture as the solvent base from the Silicone breaks the Rubbergum down.