They really do need to up their game.
I've never ordered any plants from them and never intend to.
I use local garden centres/Crocus/Sarah Raven mostly for plants.
However I do order seeds from T&M most years and have generally good results. But their prices are not cheap.
Petunia seeds which are almost invisible are just sealed into the big seed packet, so it's a case of opening the packet very carefully on 3 sides, laying it flat, then turning it over above the seed tray and do a lot of tapping and hope for the best. End result is a few patches of congested seedlings. Petunia seeds from Mr Fothergill are cheaper and usually arrive in a tiny vial and therefore much easier to sow.
Many of the plant seed descriptions on the T&M site do not give the height of the plant which is also poor. A close-up of a flower gives no idea of the height of the plant. I did mention this to their Cust Svs a few years ago, they agreed that plant height was important and should be included and said they would pass my comments on - to the bin presumably.