In the English Grammar Profile, B2 point 124 in the category of modality is defined as using:

the fixed expression ‘I must say’ to give emphasis, usually about something positive.

An iWeb search for I must say * * * *

1 I MUST SAY THAT I AM VERY 144

EU-Startups

“Computer vision can have a big impact on the fashion …

I must say that I am very happy with how the complete team of Pixyle.ai adapted to working remotely. We were up and running from day 2.

2 I MUST SAY , THOUGH , THAT 93
3 I MUST SAY , HOWEVER , THAT 89
4 I MUST SAY I AM VERY IMPRESSED 82
5 I MUST SAY THAT I DO N’T 75
6 I MUST SAY THAT I AM NOT 73
7 I MUST SAY THAT I WAS VERY 71
8 I MUST SAY YOU HAVE DONE A 68
9 I MUST SAY THAT I HAVE NEVER 66
10 I MUST SAY I WAS A LITTLE 63
11 I MUST SAY THIS IS ONE OF 61
12 I MUST SAY THAT THIS IS A 59
13 I MUST SAY I WAS VERY IMPRESSED 57
14 I MUST SAY THAT THIS IS THE 56
15 I MUST SAY THAT IT IS A 50
16 I MUST SAY I AM IMPRESSED . 49
17 I MUST SAY I AM VERY PLEASED 48
18 I MUST SAY I WAS PLEASANTLY SURPRISED 48

I must say I was pleasantly surprised by the sign language used when the Mazie and the Bird Girl Trio sang.

broadwayworld.com

19 I MUST SAY THAT IT WAS A 48
20 I MUST SAY THAT I HAVE BEEN 47
21 I MUST SAY , I AM VERY 46
22 I MUST SAY THAT YOUVE DONE A 46
23 I MUST SAY THAT THIS IS ONE 45
24 I MUST SAY THIS IS THE BEST 45
25 I MUST SAY THAT I AM IMPRESSED 44
26 I MUST SAY I WAS A BIT 43
27 I MUST SAY THAT I AGREE WITH 43
28 I MUST SAY THAT I DO NT 42
29 I MUST SAY , IT ‘S A 41
30 I MUST SAY I AM IMPRESSED WITH 41
31 I MUST SAY I WAS IMPRESSED WITH 41
32 I MUST SAY THAT I DO NOT 41
33 I MUST SAY , IT WAS A 40
34 I MUST SAY , THIS IS A 40
35 I MUST SAY THAT I AM A 40
36 I MUST SAY THAT I LOVE THE 40
37 I MUST SAY , THIS IS THE 39
38 I MUST SAY , I DO N’T 38
39 I MUST SAY , I WAS VERY 36
40 I MUST SAY I ‘M VERY IMPRESSED 36
41 I MUST SAY THAT I LIKE THE 36
42 I MUST SAY , IT IS A 33
43 I MUST SAY I AM VERY HAPPY 33
44 I MUST SAY IT WAS HARD TO 33
45 I MUST SAY THAT I WAS A 32
46 I MUST SAY , I WAS A 31
47 I MUST SAY , I ‘M VERY 30
48 I MUST SAY THAT I ‘M VERY 30
49 I MUST SAY THAT I AM EXTREMELY 30
50 I MUST SAY THAT IT HAS BEEN 30
51 I MUST SAY THAT I AM REALLY 29
52 I MUST SAY I ‘M IMPRESSED . 28
53 I MUST SAY THAT I ‘M NOT 28
54 I MUST SAY , I ‘M NOT 27
55 I MUST SAY , I HAVE BEEN 27
56 I MUST SAY I ‘M A LITTLE 27
57 I MUST SAY I LOVE IT . 27
58 I MUST SAY THAT I ABSOLUTELY LOVE 27
59 I MUST SAY , I AM NOT 26
60 I MUST SAY , I DO NT 26
61 I MUST SAY . Q! Q! Q! 25
62 I MUST SAY I AM QUITE IMPRESSED 25
63 I MUST SAY THAT I HAVE NOT 25
64 I MUST SAY THIS IS A GREAT 25
65 I MUST SAY , I AM IMPRESSED 24
66 I MUST SAY , I LOVE IT 24
67 I MUST SAY , THIS IS ONE 24
68 I MUST SAY I AM A BIT 24
69 I MUST SAY I AM A LITTLE 24
70 I MUST SAY THAT I AM QUITE 24
71 I MUST SAY THAT I WAS PLEASANTLY 24
72 I MUST SAY I LOVE IT ! 23
73 I MUST SAY IT WAS A GREAT 23
74 I MUST SAY THAT I ‘M IMPRESSED 23
75 I MUST SAY THAT I FIND IT 23
76 I MUST SAY THAT I REALLY LIKE 22
77 I MUST SAY THAT I WAS IMPRESSED 22
78 I MUST SAY THAT IT IS THE 22
79 I MUST SAY , I AM A 21
80 I MUST SAY , I DID N’T 21
81 I MUST SAY A BIG THANK YOU 21
82 I MUST SAY I ‘M VERY HAPPY 21
83 I MUST SAY IT IS THE BEST 21
84 I MUST SAY THAT I AM SO 21
85 I MUST SAY THAT I DID NOT 21
86 I MUST SAY THAT I HAVE A 21
87 I MUST SAY THAT I WAS NOT 21
88 I MUST SAY THAT I WAS QUITE 21
89 I MUST SAY THAT IT ‘S A 21
90 I MUST SAY THAT IT IS VERY 21
91 I MUST SAY THIS IS A VERY 21
92 I MUST SAY , I ‘M A 20
93 I MUST SAY IT IS ONE OF 20
94 I MUST SAY THAT I AM SURPRISED 20
95 I MUST SAY THAT I CAN NOT 20
96 I MUST SAY THAT I WAS SURPRISED 20
97 I MUST SAY , I HAVE NEVER 19
98 I MUST SAY , I LOVE THE 19
99 I MUST SAY , I REALLY LIKE 19
100 I MUST SAY , I WAS IMPRESSED 19

B1 vocabulary in the above lines:

absolutely, extremely, pleasantly, though
B2:
impressed