Anyone else running a cheap Chinese MPPT off a single 100W panel? Curious what you're actually getting

I picked up a Renogy Wanderer 30A off eBay for £18 (used, but tested fine) and paired it with a knackered-looking 100W poly panel I grabbed from a Facebook Marketplace bloke in Coventry for a tenner. Wired it into a 100Ah leisure battery I already had kicking around. Total outlay: about £30 quid for the new bits, which felt ridiculous.

Honest results have been... decent? On a clear day last week I was seeing peaks of around 4.5–5A charge current, which works out to roughly 55–60W real-world output. Not the full 100W obviously, but I wasn't expecting miracles from a second-hand poly panel that's probably seen better days. The Wanderer's readout seems plausible enough, though I've no idea how accurate it actually is.

What I'm wondering is whether anyone's bothered adding a proper inline ammeter or a shunt monitor to double-check what these cheap controllers are actually reporting. I've seen the DROK inline meters on Amazon for about £8–12 — are they worth it, or is the margin of error on those just as bad? Would love to know what others are genuinely measuring versus what their controller claims.

@DanPhillips that's a cracking deal on the Wanderer!

Quick question though — when you say the panel looked "knackered," did you actually test the open-circuit voltage before wiring it up? I've got a couple of dodgy secondhand panels on my static caravan setup and one of them had a delaminated backsheet that was causing all sorts of weird readings on my Victron SmartSolar.

Also curious — what battery are you charging into? I'm wondering whether a 30A controller is overkill for a single 100W panel (theoretical max is what, ~6A?), or are you planning to add more panels later?

I ask because I nearly bought an oversized controller myself and somebody on here pointed out I was wasting money on capacity I'd never use — though I suppose having headroom for expansion isn't the worst thing?