It sounds like you're considering the C200, and it just so happens I have one. Below is a copy and paste from another thread I replied to on here, and I've added a bit more. I don't remember if there are 2 versions; one for a round bowl and one for an elongated bowl. You'll want the elongated, and of course the elongated Aquia.
Recently installed a Toto C200 as part of a complete master bath remodel. It is perched atop a Toto Aquia 1.6/0.8 wall mounted bowl hung on a Geberit carrier (the plumbing connection between the two was a headache for a noob like me. I'll get to that.).
I don't know what the feature differences are between the G400 you're considering and the C200. I do know the C200 has an in-line water heater which makes the physical dimensions of the whole unit smaller, sleeker. Heated seat (soft close but not motorized), heated air dryer (if you have the time to wait), various spray patterns, adjustable pressure and temp, memory for two different set ups, wall mounted remote (I didn't care for the seat side mounted set ups). Also has the bowl pre-wash down. The seat might be a little thicker due to the heating element but it's negligible.
Everyone's bum is different, but the C200 works well for us. I sometimes shift forward a bit to ensure...thoroughness but that's about it. Spouse has no issue with it. The bowl wash down does seem to work quite effectively but, again, different people present different....challenges.
It makes noises that I don't understand. For instance, after any usage, even after just sitting on it, it emits 3 short "hums", each spaced...I dunno, maybe 20 seconds apart. Then they stop, but the unit isn't finished yet because there remains a very, very quite but persistent hum, almost sounds like a very low speed cooling fan. Though I've not timed it, it does carry on for probably over 30 minutes. The good news is unless you're listening for it you're not likely to notice it, and you definitely won't if you're in an adjacent room. Regardless, mine does not run any wash cycles at any time other than when you first sit on it. Ever.
Why, whyyyyy Toto doesn't make these things with field replaceable power cords is a mystery. My unit came with a 3.5-4' long cord. If you're doing a extensive remodel, or a new build, and put an outlet close by, you're then left with a bundle of cord. Both Toto and Geberit specify where to place the outlet in the install instructions for their respective carriers but there is no physical reason you have to put it where they say, so long as it's within reach of the cord. If you do put it where Geberit says you have to deal with the excessive cord length in one way or another. I ended up cutting/splicing/soldering/and white heat shrinking mine.
As well, both Toto and Geberit specify where the water connection needs to go for their carriers, and Geberit offers a bidet water connection kit (Geberit does sell bidet seats in other parts of the world, but not in the US. Go figure.) The kit P/N is 249.801.00.1. The assembly consists of a braided SS hose, a mounting plate, and a 1/2" female opening - it's all one piece. The hose snakes up though a plastic conduit that's already installed on the carrier, and connects to the tanks' integrated water shut off valve via a "Y" adapter (comes with the kit). Geberit sells a shut off valve for the outlet connection but don't bother, because...
...the Toto bidet water supply hose connector is proprietary. It is not a standard 1/4" screw on affair so you cannot use a typical off the shelf 1/4" angle stop. You MUST use their special valve, P/N THU468 I believe (I don't recall if one comes with the C200). If you call Toto, as I did, they'll tell you that's the valve you need, but they don't tell you that you also need a 1/2" male nipple (I used a 1.5") to mate their valve to the Geberit connector, and of course the nipple does not come with the valve. But you're not done with the fun yet.
Look at the picture of the Geberit water supply kit. You'll see the rectangular mounting plate gets attached to the finished wall with two screws. I wanted the supply hose to run a certain way in order to keep things as tidy as possible and to ensure the connectors at both ends of the hose were not under stress, so the Toto valve outlet needed to be "clocked" (mine is at 5 o'clock). To achieve this you'll need to preassemble everything first and mock it all up. I did have a tough time getting the nipple to seal in the Geberit fitting - couldn't quite tell if the threads in the fitting are straight or NPT. Regardless, enough Teflon tape sealed it.
Pictures added by Terry Love