Welcome to the forum.
No experience of the Avon Adventure 450, but suspect as you've said it will have a shallow V hull and isn't anywhere as robust as Seariders. The Zodiac Pro 420 (used to own one), is a capable boat, but again it's a shallow V hull, so will slap when it gets rough. If you were out yourself - then you'd need a couple of bags of sand up front in the bow locker. I had it with a console and rear bench seat and fine two-up.
One of the benefits of the Zodiac is a slide-on tube-set, so you can completely replace it and have a new boat, although be warned, Zodiac prices are expensive.
One thing to watch is - the console has a very light lay-up of fibre-glass, so check for tell-tale stress cracks. Mostly superficial, but something to be aware of.