Videogame Perfection is out of stock, but Castlemania Games is taking pre-orders and expecting to ship in mid april. You'll save a bit not having to pay the currency conversion and international shipping.
The RetroTink2x and OSSC are in and out of stock, they sell out because they're niche items made to order in small-ish batches. Not quite as sought after as the UltraHDMI mod for the N64 (I had to wait 4 months for mine), but niche in a similar way. Most people will just buy one of those cheap converters on amazon and never look back. There's nothing wrong picking an inexpensive solution if lag and poor picture quality aren't deal breakers. For me they are. That's how I came across the OSSC and RetroTink2x.