We had a trip out on the Tidal Thames last weekend launching at Putney Bridge.
It's 'do-able' and yes the currents are strong, water is 'lumpy' the further you head East but the major factors I'd consider are No1 Debris and No2 Traffic.
Keep your eyes on the traffic coming from all around you and at high speed!
Most importantly have a sharp knife onboard and a repair kit!!! as my OB failed 3 times with crap wrapped around the prop and an accompanying boat had the same happen twice.
At one point the accompanying boat was lifted out of the water and the OB nearly torn off
The amount of debris within the water is disgustingly high on all levels, rope, plastic binding, plastic bags, pallets, logs 8ft in length, scaffold boards, lengths of timber with nails in, cans, bottles, oil drums.........the list goes on and on.
Loved the sights of London from the water but I'll never revisit 'Tidal Thames' ever again
A great shame the Thames is in such a mess