Shower Pan / Toilet Holding Tank Combo

Started a new build which will include a drop floor down the center but a sit down shower and toilet at regular floor height.
I have found, but not yet acquired, a combination shower pan and toilet holding tank. The unit includes a toilet flange and vent fitting topside and separate bottom drains for the shower and holding tank. There are models available with side drains rather than in the center. All else needed would be a low rise toilet, gray-water holding tank for the shower, three waterproof walls, and a shower door or curtain, and hand held shower head.
Has anybody used this or a similar product? I know some have built there own using fibreglass and/or tile.

The shower will drain into a dedicated holding tank - would a trap be needed?
I have found, but not yet acquired, a combination shower pan and toilet holding tank. The unit includes a toilet flange and vent fitting topside and separate bottom drains for the shower and holding tank. There are models available with side drains rather than in the center. All else needed would be a low rise toilet, gray-water holding tank for the shower, three waterproof walls, and a shower door or curtain, and hand held shower head.
Has anybody used this or a similar product? I know some have built there own using fibreglass and/or tile.

The shower will drain into a dedicated holding tank - would a trap be needed?