It seems that spot forex at IB have switched from half pips to tenth pips not so long ago.
If you are a live client, would you mind posting a couple screenshots of the order book on the majors, EUR/USD and GBP/USD especially , or just comment what's the average liquidity to be expected on average for each tenth pip line, and spreads nowadays.

I also understand that the model is the ECN type, not exchange (LMAX type) with the risk to get last look slippage from liquidity providers on top of latency and liquidity slippage.
If you have traded there for a long time, are you satisfied with the quality of executions overall ?

IB does not seem to be a leader for spot fx, regarding monthly traded volumes, so I'm wondering if it's worth it.
I know about the pitfalls already : 100ms snapshot data, data requests limitations and the need to convert manually the currencies' PnL when they do not happen to be in your account base currency.

Are the statements clearly understandable for an accountant or not the best ? Can you print monthly summaries ?

IB will show you the exact liquidity offered on the depth of market and obviously at the bid and ask. More importantly, most of the liquidity is actually at half pips, i.e. .00005. Typically there's at least $2M-$5M on the majors at any given moment during London or NY.

For all the "drawbacks" that you mentioned, the execution tends to be spot on and rarely will you get hit by "off quotes" to take out orders that don't actually trade through your price because of spread issues by less reputable brokers.