Most places charge ridiculous prices for tiny tubes of silicone grease. But I got a 500g tub from a plumber's merchant for less than £10 ages ago. I don't know what the price would be now, as I'm still using the original tub
Just to be clear, I use the silicone grease to give a light coating on the seals and grooves, to make sure they seat properly. Then I wet the cylinder walls and piston with clean brake fluid before assembly. As well as lubricating the piston, it helps free air bubbles from sticking to the dry surfaces, especially the rough-cast base of the cylinder. It's surprising how much air can be held this way; I leave the assembled calipers full of fluid for a while, to let all the bubbles rise to the bleed nipple, before pushing the pistons fully home and expelling the fluid. After a first ride, I bleed them again; there's often still a tiny bubble or two in there.
As far as I know, the red grease is only intended for rubber components, it's not meant to be used as a lubricant for metal-to-metal parts. The same goes for silicone grease. For metal-to-metal moving parts, stick to the conventional petroleum based greases.
One issue with grease on metal brake parts is that the high temperatures will soften or melt it, risking contamination of the friction lining. Some manufacturers avoid this by assembling dry, others use minimal coatings of high-melting point grease, on critical areas only, such as anti-sqeal shims and the sliding faces of the pad carriers or pins. I prefer to use copperslip on steel parts, but that is said to cause corrosion on ali components, so be careful with it. Whatever you put on, winter salt and grime will get in there, and no grease is a substitute for regular cleaning. And with the crappy cast cheese Nissin use, that means an annual strip down.
All the above is a personal view; as has already been said, make your own mind up, and if in doubt, get professional advice or get a professional to do it for you. You could try calling Bigg Red; I've always found them helpful, and as they service most makes, they must be aware of the conflicting views.