No, they aren't.
1- They are paid too late. I understand why SFE want proof of attendance, but universities will ask for accomadation deposits (and sometimes the first rent payment!) before the first payment will be recieved. Also, the equiptment/textbooks universities ask students to buy will often cost £100-300, even if bought second hand. Many 18 year olds don't have access to, say £600 before they've even started. This puts students from less well off backgrounds at an imediate disadvantage.
2- They often aren't enough to live on, once rent has been taken into account. Rent in halls is often very high, and even renting a room in a shared house is more expensive in student areas. Being charged £5000 for halls is not uncommon. This leaves the majority of students reliant on family support or getting a part time job. Even with the maximum loan/grant available, a student would struggle to absorb an unexpected emergancy cost.
3- Household income is an inadequate way of means testing for all sorts of reasons. It's also wrong to expect parents to support their adult children who have left home.
4- The system of applying is pretty complicated and off-putting. Staff at call centres often give conflicting advice. The system is very slow moving if you have a change of circumstance. Ultimately, this results in late payment of loans for students, meaning they can end up facing real financial hardship.
I think a standardised maintenence loan, for all students, is fairest. It should absolutely cover the cost of living (including a small emergancy fund) and being able to buy all course materials. The application process would then be simplified. First year students should get an advance on their loan paid when they complete online enrollment at their university, so they can put a deposit down on accomadation and buy everything they need for uni.