Honestly, Terapeak is the most accurate since it's eBay's own data, but I totally get why you hate the mobile interface. It's kinda a hot mess on a small screen. For flipping vintage Casios in the UK, you actually have a few solid options that aren't just for sports cards.

• 130point actually works for almost any category. It's definitely not just for cards. The big win there is seeing the actual Best Offer price. eBay hides that on their own site usually, but 130point pulls the real number. Super handy for those weird rare Casio models where sellers list for 200 quid but accept 120.
• CheckAFlip is a bit old school and the site looks like it's from 2005, but it gives a quick average of sold vs. unsold prices. It's decent for a fast gut check when you're standing in a cold car boot sale and need to decide in five seconds.
• The eBay mobile app Sold Items filter is honestly what I use 90% of the time for speed. Just tap Filter, then Show More, then Sold Items. It's faster than any third party tool when you're on the move.
• WorthPoint is the nuclear option. It's pricey (about 20 pounds a month) but it goes back years. Probably not worth it for basic Casios, but if you find a rare Marlin or something, it might pay for itself. I usually just stick to the eBay app for the quick stuff and then 130point if I think a Best Offer was used on a high value piece. Its way faster than trying to load Terapeak on a phone.