TiLFA
No Need for TLDP session. R2 will stack two labels, Node SID of R6 and Top label as Node SID label of R4. Its brings a simplicity with using TLDP session.
Double segment protection : No overlap of any PQ space. TiLFA can provide coverage in these kind of situations by steering the packet from P Space to Q Space nodes.
Lets take an example : adj SID of 24065 for R5-R6 link. Then R2 can perform three label stack with first labels are used to steer the packet from P to Q space node and third label will be destination prefix SID label.
Path Optimality
Another thing which TiLFA brings is the path optimally from PLR perspective. TiLFA always prefers the post convergence path from a PLR point view.
In case RSVP TE FRR (Link Protection, facility backup) traffic circle all the way back to the next hop (P5). Obviously its sub optimal but its temporary condition till the headed PE1 realize about the failure.
In case of LFA, you can see that the path goes via P4-P2 link with a higher metric. Considering that metrics represent bandwidth of a link in a network, in the event of failure traffic will be going through bandwidth links bandwidth which could cause congestion and packet drop on the low capacity link.
TiLFA its possible for the PLR. P4 to use the post convergence path which is via P1-P2-P3-PE2.
PLR sends a packet with two label stack to get to P2 and the inner prefix sid for the destination. Path for P2 and P4 perspective is via P1. When P1 sees the top label for P2, its pops the label and send it towards P2 and from there you already know it will follow all the way to the destination. So you can see in the case of TiLFA the optimal path is used from the perspective of PLR.
Excellent Bhai